diff --git a/packages/page-controller/src/dom/dom_tree/dropdown-cap.test.ts b/packages/page-controller/src/dom/dom_tree/dropdown-cap.test.ts
new file mode 100644
index 000000000..690940e17
--- /dev/null
+++ b/packages/page-controller/src/dom/dom_tree/dropdown-cap.test.ts
@@ -0,0 +1,103 @@
+import { beforeEach, describe, expect, it } from 'vitest'
+
+import { flatTreeToString } from '../index'
+import domTree from './index.js'
+
+function setupSizes() {
+	Object.defineProperty(HTMLElement.prototype, 'offsetWidth', {
+		configurable: true,
+		get() {
+			return 100
+		},
+	})
+	Object.defineProperty(HTMLElement.prototype, 'offsetHeight', {
+		configurable: true,
+		get() {
+			return 30
+		},
+	})
+}
+
+function buildDropdown(html: string) {
+	return domTree({
+		doHighlightElements: false,
+		viewportExpansion: -1,
+		interactiveBlacklist: [],
+		interactiveWhitelist: [],
+	}) as any
+}
+
+describe('dropdown option cap (#348)', () => {
+	beforeEach(() => {
+		setupSizes()
+		document.body.innerHTML = ''
+	})
+
+	it('indexes at most 20 options per dropdown container', () => {
+		const options = Array.from(
+			{ length: 25 },
+			(_, i) => `<li class="el-select-dropdown__item" style="cursor:pointer">选项 ${i}</li>`
+		)
+		document.body.innerHTML = `
+			<div class="el-select-dropdown">
+				<ul class="el-select-dropdown__list">${options.join('')}</ul>
+			</div>
+		`
+		const tree = buildDropdown(document.body.innerHTML)
+		const liNodes = Object.values(tree.map).filter((n: any) => n.tagName === 'li')
+		const indexed = liNodes.filter((n: any) => typeof n.highlightIndex === 'number')
+		expect(indexed.length).toBe(20)
+	})
+
+	it('records dropped options on the container', () => {
+		const options = Array.from(
+			{ length: 25 },
+			(_, i) => `<li class="el-select-dropdown__item" style="cursor:pointer">选项 ${i}</li>`
+		)
+		document.body.innerHTML = `
+			<div class="el-select-dropdown">
+				<ul class="el-select-dropdown__list">${options.join('')}</ul>
+			</div>
+		`
+		const tree = buildDropdown(document.body.innerHTML)
+		const container = Object.values(tree.map).find(
+			(n: any) => n.tagName === 'div' && n.extra?.droppedOptions === 5
+		)
+		expect(container).toBeDefined()
+	})
+
+	it('renders a folded-options hint in the simplified HTML', () => {
+		const options = Array.from(
+			{ length: 25 },
+			(_, i) => `<li class="el-select-dropdown__item" style="cursor:pointer">选项 ${i}</li>`
+		)
+		document.body.innerHTML = `
+			<div class="el-select-dropdown">
+				<ul class="el-select-dropdown__list">${options.join('')}</ul>
+			</div>
+		`
+		const tree = buildDropdown(document.body.innerHTML)
+		const html = flatTreeToString(tree)
+		expect(html).toContain('5 more option(s) not shown')
+		// only the first 20 options carry indexes
+		expect(html).toContain('[19]<li >选项 19')
+		expect(html).not.toContain('选项 24')
+	})
+
+	it('does not cap dropdowns with few options', () => {
+		const options = Array.from(
+			{ length: 6 },
+			(_, i) => `<li class="el-select-dropdown__item" style="cursor:pointer">选项 ${i}</li>`
+		)
+		document.body.innerHTML = `
+			<div class="el-select-dropdown">
+				<ul class="el-select-dropdown__list">${options.join('')}</ul>
+			</div>
+		`
+		const tree = buildDropdown(document.body.innerHTML)
+		const liNodes = Object.values(tree.map).filter((n: any) => n.tagName === 'li')
+		expect(liNodes.filter((n: any) => typeof n.highlightIndex === 'number').length).toBe(6)
+		const html = flatTreeToString(tree)
+		expect(html).not.toContain('not shown')
+	})
+})
diff --git a/packages/page-controller/src/dom/dom_tree/dropdown-options.test.ts b/packages/page-controller/src/dom/dom_tree/dropdown-options.test.ts
new file mode 100644
index 000000000..c027c0a41
--- /dev/null
+++ b/packages/page-controller/src/dom/dom_tree/dropdown-options.test.ts
@@ -0,0 +1,79 @@
+import { beforeEach, describe, expect, it } from 'vitest'
+
+import domTree from './index.js'
+
+function setupSizes() {
+	Object.defineProperty(HTMLElement.prototype, 'offsetWidth', {
+		configurable: true,
+		get() {
+			return 100
+		},
+	})
+	Object.defineProperty(HTMLElement.prototype, 'offsetHeight', {
+		configurable: true,
+		get() {
+			return 30
+		},
+	})
+}
+
+function buildDropdown(html: string) {
+	return domTree({
+		doHighlightElements: false,
+		viewportExpansion: -1,
+		interactiveBlacklist: [],
+		interactiveWhitelist: [],
+	}) as any
+}
+
+function getIndexedOptions(tree: any) {
+	return Object.values(tree.map)
+		.filter((n: any) => n.tagName === 'li' && typeof n.highlightIndex === 'number')
+		.sort((a: any, b: any) => a.highlightIndex - b.highlightIndex)
+}
+
+describe('dropdown option indexing (#519)', () => {
+	beforeEach(() => {
+		setupSizes()
+		document.body.innerHTML = ''
+	})
+
+	it('indexes enabled dropdown options', () => {
+		document.body.innerHTML = `
+			<div class="el-select-dropdown">
+				<ul class="el-select-dropdown__list">
+					<li class="el-select-dropdown__item" style="cursor:pointer">选项1</li>
+					<li class="el-select-dropdown__item" style="cursor:pointer">选项2</li>
+					<li class="el-select-dropdown__item" style="cursor:pointer">选项3</li>
+				</ul>
+			</div>
+		`
+		const tree = buildDropdown(document.body.innerHTML)
+		const indexed = getIndexedOptions(tree)
+		expect(indexed.length).toBe(3)
+	})
+
+	it('indexes disabled dropdown options so the full list is visible to the LLM', () => {
+		document.body.innerHTML = `
+			<div class="el-select-dropdown">
+				<ul class="el-select-dropdown__list">
+					<li class="el-select-dropdown__item" style="cursor:pointer">闸片产线</li>
+					<li class="el-select-dropdown__item is-disabled" style="cursor:not-allowed">落料车间</li>
+					<li class="el-select-dropdown__item" style="cursor:pointer">机加车间</li>
+				</ul>
+			</div>
+		`
+		const tree = buildDropdown(document.body.innerHTML)
+		const indexed = getIndexedOptions(tree)
+		expect(indexed.length).toBe(3)
+	})
+
+	it('still excludes disabled buttons outside dropdowns', () => {
+		document.body.innerHTML = `
+			<button style="cursor:not-allowed" disabled>保存</button>
+		`
+		const tree = buildDropdown(document.body.innerHTML)
+		const buttons = Object.values(tree.map).filter((n: any) => n.tagName === 'button')
+		expect(buttons.every((n: any) => n.highlightIndex === undefined)).toBe(true)
+	})
+})
diff --git a/packages/page-controller/src/dom/dom_tree/index.js b/packages/page-controller/src/dom/dom_tree/index.js
index 7f6b3afd3..d3f222529 100644
--- a/packages/page-controller/src/dom/dom_tree/index.js
+++ b/packages/page-controller/src/dom/dom_tree/index.js
@@ -687,6 +687,54 @@ export default (
 		)
 	}
 
+	/**
+	 * @edit dropdown/menu option detection
+	 * li/option elements (or role=option/menuitem/listitem) inside a dropdown or menu
+	 * container are treated as indexable even when visually disabled (cursor: not-allowed),
+	 * so the LLM sees the complete option list.
+	 */
+	const DROPDOWN_OPTION_ROLES = new Set([
+		'option',
+		'menuitem',
+		'menuitemradio',
+		'menuitemcheckbox',
+		'listitem',
+	])
+	const DROPDOWN_CONTAINER_SELECTOR = [
+		'[role="listbox"]',
+		'[role="menu"]',
+		'[role="menubar"]',
+		'select',
+		'.el-select-dropdown',
+		'.el-dropdown-menu',
+		'[data-toggle="dropdown"]',
+	].join(', ')
+
+	function isDropdownOptionElement(element) {
+		if (!element || element.nodeType !== Node.ELEMENT_NODE) return false
+		const tagName = element.tagName.toLowerCase()
+		const role = element.getAttribute('role')
+		if (tagName !== 'li' && tagName !== 'option' && !(role && DROPDOWN_OPTION_ROLES.has(role))) {
+			return false
+		}
+		return Boolean(element.closest(DROPDOWN_CONTAINER_SELECTOR))
+	}
+
+	/**
+	 * @edit cap dropdown options per container (#348)
+	 * A select/dropdown with hundreds of options would blow up the LLM payload;
+	 * index at most MAX_DROPDOWN_OPTIONS_PER_CONTAINER options and fold the rest
+	 * into a hint on the container.
+	 */
+	const MAX_DROPDOWN_OPTIONS_PER_CONTAINER = 20
+	const dropdownOptionCounts = new WeakMap() // container element -> indexed option count
+
+	function getDropdownOptionContainer(element) {
+		if (!element || element.nodeType !== Node.ELEMENT_NODE) return null
+		if (!isDropdownOptionElement(element)) return null
+		return element.closest(DROPDOWN_CONTAINER_SELECTOR)
+	}
+
 	/**
 	 * Checks if an element is interactive.
 	 *
@@ -711,6 +759,15 @@ export default (
 			return true // Skip whitelisted elements
 		}
 
+		/**
+		 * @edit dropdown options should stay indexable even when disabled,
+		 * otherwise the LLM cannot see or select the full option list
+		 * (e.g. Element UI / Avue selects with disabled options).
+		 */
+		if (isDropdownOptionElement(element)) {
+			return true
+		}
+
 		// Cache the tagName and style lookups
 		const tagName = element.tagName.toLowerCase()
 		const style = getCachedComputedStyle(element)
@@ -1635,6 +1692,24 @@ export default (
 			if (nodeData.isVisible) {
 				nodeData.isTopElement = isTopElement(node)
 
+				/**
+				 * @edit cap dropdown options per container (#348)
+				 * A dropdown with hundreds of options would blow up the LLM payload;
+				 * index at most MAX_DROPDOWN_OPTIONS_PER_CONTAINER options per container
+				 * and fold the excess into a hint on the container.
+				 */
+				if (isDropdownOptionElement(node)) {
+					const container = getDropdownOptionContainer(node)
+					const used = dropdownOptionCounts.get(container) || 0
+					if (used >= MAX_DROPDOWN_OPTIONS_PER_CONTAINER) {
+						addExtraData(container, {
+							droppedOptions: (extraData.get(container)?.droppedOptions || 0) + 1,
+						})
+						return null // Skip excess options entirely (text included)
+					}
+					dropdownOptionCounts.set(container, used + 1)
+				}
+
 				// Special handling for ARIA menu containers - check interactivity even if not top element
 				const role = node.getAttribute('role')
 				const isMenuContainer = role === 'menu' || role === 'menubar' || role === 'listbox'
diff --git a/packages/page-controller/src/dom/index.ts b/packages/page-controller/src/dom/index.ts
index a7ae7f8ee..66192b31c 100644
--- a/packages/page-controller/src/dom/index.ts
+++ b/packages/page-controller/src/dom/index.ts
@@ -432,6 +432,14 @@ export function flatTreeToString(
 				processNode(child, nextDepth, result)
 			}
 
+			/**
+			 * @edit dropdown options are capped per container (#348);
+			 * render a hint so the LLM knows more options exist.
+			 */
+			if (node.extra?.droppedOptions) {
+				result.push(`${depthStr}... ${node.extra.droppedOptions} more option(s) not shown ...`)
+			}
+
 			if (emitSemantic) {
 				// empty tag should be removed
 				if (result.length === mark + 1) {