diff --git a/src/routes/admin/posts/[id]/+page.svelte b/src/routes/admin/posts/[id]/+page.svelte
index 1e1df35..434ae61 100644
--- a/src/routes/admin/posts/[id]/+page.svelte
+++ b/src/routes/admin/posts/[id]/+page.svelte
@@ -53,6 +53,30 @@
 	let isAddingTag = $state(false);
 	let showTagDropdown = $state(false);
 
+	let tagInputContainer = $state<HTMLDivElement>();
+	let tagDropdownTop = $state(0);
+	let tagDropdownBottom = $state(0);
+	let tagDropdownLeft = $state(0);
+	let tagDropdownWidth = $state(0);
+	let tagDropdownUpwards = $state(false);
+
+	function updateTagDropdownPosition() {
+		if (tagInputContainer) {
+			const rect = tagInputContainer.getBoundingClientRect();
+			const spaceBelow = window.innerHeight - rect.bottom;
+			const spaceAbove = rect.top;
+			if (spaceBelow < 200 && spaceAbove > spaceBelow) {
+				tagDropdownUpwards = true;
+				tagDropdownBottom = window.innerHeight - rect.top;
+			} else {
+				tagDropdownUpwards = false;
+				tagDropdownTop = rect.bottom;
+			}
+			tagDropdownLeft = rect.left;
+			tagDropdownWidth = rect.width;
+		}
+	}
+
 	let filteredTags = $derived(
 		(() => {
 			const input = newTagInput.trim().toLowerCase();
@@ -121,6 +145,7 @@
 	<Alert message={form.error} />
 {/if}
 
+<svelte:window onresize={() => (showTagDropdown = false)} />
 <form method="POST" action="?/update" id="post-form" class="post-form">
 	<!-- 正文由页面统一持有并始终提交，避免切到「预览」时编辑器卸载导致正文丢失 -->
 	<input type="hidden" name="content" value={content} />
@@ -172,7 +197,7 @@
 			</div>
 		</div>
 
-		<div class="form-sidebar">
+		<div class="form-sidebar" onscroll={() => (showTagDropdown = false)}>
 			<EditorSidebarTabs {outline} bind:activeTab={sidebarTab} />
 
 			<!-- 设置面板始终挂载（仅切换显隐），确保别名/分类/系列/标签等字段在提交时始终存在 -->
@@ -244,14 +269,17 @@
 						{/each}
 					</div>
 
-					<div class="tag-input-container">
+					<div class="tag-input-container" bind:this={tagInputContainer}>
 						<TextInput
 							type="text"
 							class="tag-input-new"
 							placeholder="+ 添加{$page.data.aliases?.tag || '标签'}..."
 							bind:value={newTagInput}
 							onkeydown={handleAddTag}
-							onfocus={() => (showTagDropdown = true)}
+							onfocus={() => {
+								updateTagDropdownPosition();
+								showTagDropdown = true;
+							}}
 							onblur={() => setTimeout(() => (showTagDropdown = false), 200)}
 							disabled={isAddingTag}
 							autocomplete="off"
@@ -259,7 +287,16 @@
 						/>
 
 						{#if showTagDropdown && filteredTags.length > 0}
-							<div class="tag-autocomplete-dropdown">
+							<div
+								class="tag-autocomplete-dropdown"
+								style="top: {tagDropdownUpwards
+									? 'auto'
+									: `${tagDropdownTop}px`}; bottom: {tagDropdownUpwards
+									? `${tagDropdownBottom}px`
+									: 'auto'}; left: {tagDropdownLeft}px; width: {tagDropdownWidth}px; margin-top: {tagDropdownUpwards
+									? '0'
+									: '4px'}; margin-bottom: {tagDropdownUpwards ? '4px' : '0'};"
+							>
 								{#each filteredTags as tag (tag.id || tag)}
 									<button
 										type="button"
@@ -474,10 +511,7 @@
 	}
 
 	.tag-autocomplete-dropdown {
-		position: absolute;
-		top: 100%;
-		left: 0;
-		right: 0;
+		position: fixed;
 		background: var(--bg-color);
 		border: 1px solid var(--text-color);
 		box-shadow: 2px 2px 0 rgba(0, 0, 0, 0.15);
@@ -486,7 +520,6 @@
 		overflow-y: auto;
 		display: flex;
 		flex-direction: column;
-		margin-top: 4px;
 	}
 
 	.tag-dropdown-item {
diff --git a/src/routes/admin/posts/new/+page.svelte b/src/routes/admin/posts/new/+page.svelte
index 814227d..9ce39dd 100644
--- a/src/routes/admin/posts/new/+page.svelte
+++ b/src/routes/admin/posts/new/+page.svelte
@@ -71,6 +71,30 @@
 	let isAddingTag = $state(false);
 	let showTagDropdown = $state(false);
 
+	let tagInputContainer = $state<HTMLDivElement>();
+	let tagDropdownTop = $state(0);
+	let tagDropdownBottom = $state(0);
+	let tagDropdownLeft = $state(0);
+	let tagDropdownWidth = $state(0);
+	let tagDropdownUpwards = $state(false);
+
+	function updateTagDropdownPosition() {
+		if (tagInputContainer) {
+			const rect = tagInputContainer.getBoundingClientRect();
+			const spaceBelow = window.innerHeight - rect.bottom;
+			const spaceAbove = rect.top;
+			if (spaceBelow < 200 && spaceAbove > spaceBelow) {
+				tagDropdownUpwards = true;
+				tagDropdownBottom = window.innerHeight - rect.top;
+			} else {
+				tagDropdownUpwards = false;
+				tagDropdownTop = rect.bottom;
+			}
+			tagDropdownLeft = rect.left;
+			tagDropdownWidth = rect.width;
+		}
+	}
+
 	let filteredTags = $derived(
 		(() => {
 			const input = newTagInput.trim().toLowerCase();
@@ -139,6 +163,7 @@
 	<Alert message={form.error} />
 {/if}
 
+<svelte:window onresize={() => (showTagDropdown = false)} />
 <form method="POST" id="post-form" class="post-form">
 	<!-- 正文由页面统一持有并始终提交，避免切到「预览」时编辑器卸载导致正文丢失 -->
 	<input type="hidden" name="content" value={content} />
@@ -190,7 +215,7 @@
 			</div>
 		</div>
 
-		<div class="form-sidebar">
+		<div class="form-sidebar" onscroll={() => (showTagDropdown = false)}>
 			<EditorSidebarTabs {outline} bind:activeTab={sidebarTab} />
 
 			<!-- 设置面板始终挂载（仅切换显隐），确保别名/分类/系列/标签等字段在提交时始终存在 -->
@@ -274,14 +299,17 @@
 						{/each}
 					</div>
 
-					<div class="tag-input-container">
+					<div class="tag-input-container" bind:this={tagInputContainer}>
 						<TextInput
 							type="text"
 							class="tag-input-new"
 							placeholder="+ 添加{$page.data.aliases?.tag || '标签'}..."
 							bind:value={newTagInput}
 							onkeydown={handleAddTag}
-							onfocus={() => (showTagDropdown = true)}
+							onfocus={() => {
+								updateTagDropdownPosition();
+								showTagDropdown = true;
+							}}
 							onblur={() => setTimeout(() => (showTagDropdown = false), 200)}
 							disabled={isAddingTag}
 							autocomplete="off"
@@ -289,7 +317,16 @@
 						/>
 
 						{#if showTagDropdown && filteredTags.length > 0}
-							<div class="tag-autocomplete-dropdown">
+							<div
+								class="tag-autocomplete-dropdown"
+								style="top: {tagDropdownUpwards
+									? 'auto'
+									: `${tagDropdownTop}px`}; bottom: {tagDropdownUpwards
+									? `${tagDropdownBottom}px`
+									: 'auto'}; left: {tagDropdownLeft}px; width: {tagDropdownWidth}px; margin-top: {tagDropdownUpwards
+									? '0'
+									: '4px'}; margin-bottom: {tagDropdownUpwards ? '4px' : '0'};"
+							>
 								{#each filteredTags as tag (tag.id || tag)}
 									<button
 										type="button"
@@ -504,10 +541,7 @@
 	}
 
 	.tag-autocomplete-dropdown {
-		position: absolute;
-		top: 100%;
-		left: 0;
-		right: 0;
+		position: fixed;
 		background: var(--bg-color);
 		border: 1px solid var(--text-color);
 		box-shadow: 2px 2px 0 rgba(0, 0, 0, 0.15);
@@ -516,7 +550,6 @@
 		overflow-y: auto;
 		display: flex;
 		flex-direction: column;
-		margin-top: 4px;
 	}
 
 	.tag-dropdown-item {