diff --git a/ai_knowledge_base_v2/apps/admin-web/src/components/StreamingMarkdownMessage.vue b/ai_knowledge_base_v2/apps/admin-web/src/components/StreamingMarkdownMessage.vue
index 18ce47d..b466758 100644
--- a/ai_knowledge_base_v2/apps/admin-web/src/components/StreamingMarkdownMessage.vue
+++ b/ai_knowledge_base_v2/apps/admin-web/src/components/StreamingMarkdownMessage.vue
@@ -13,7 +13,15 @@ const markdown = new MarkdownIt({ breaks: true, html: false, linkify: true });
 const parsed = computed(() => splitReasoning(props.content));
 const answer = computed(() => parsed.value.answer.replace(/^\s+/, ""));
 const reasoning = computed(() => props.reasoning || parsed.value.reasoning);
-const renderedContent = computed(() => answer.value.trim() ? markdown.render(answer.value) : "");
+const renderedContent = computed(() => answer.value.trim() ? markdown.render(normalizeStandaloneHeadings(answer.value)) : "");
+
+function normalizeStandaloneHeadings(content: string) {
+  return content.replace(/^([ \t]*)\*\*(.+)\*\*[ \t]*$/gm, (line, indent: string, title: string) => {
+    const normalizedTitle = title.trim();
+    if (!normalizedTitle || normalizedTitle.length > 48 || normalizedTitle.includes("**")) return line;
+    return `${indent}### ${normalizedTitle}`;
+  });
+}
 
 function splitReasoning(content: string) {
   const lower = content.toLowerCase();
diff --git a/ai_knowledge_base_v2/apps/admin-web/src/styles.css b/ai_knowledge_base_v2/apps/admin-web/src/styles.css
index d094ebf..a0bac47 100644
--- a/ai_knowledge_base_v2/apps/admin-web/src/styles.css
+++ b/ai_knowledge_base_v2/apps/admin-web/src/styles.css
@@ -1384,38 +1384,43 @@ textarea {
   overflow-wrap: anywhere;
   color: #263832;
   font-size: 14px;
-  line-height: 1.75;
+  line-height: 1.68;
 }
 
 .agent-preview-markdown > :first-child { margin-top: 0; }
 .agent-preview-markdown > :last-child { margin-bottom: 0; }
-.agent-preview-markdown p { margin: 0 0 10px; }
+.agent-preview-markdown p { margin: 0 0 8px; }
 
 .agent-preview-markdown h1,
 .agent-preview-markdown h2,
 .agent-preview-markdown h3,
-.agent-preview-markdown h4 {
-  margin: 16px 0 8px;
+.agent-preview-markdown h4,
+.agent-preview-markdown h5,
+.agent-preview-markdown h6 {
+  margin: 13px 0 5px;
   color: #1f352e;
-  line-height: 1.45;
+  line-height: 1.42;
+  font-weight: 700;
 }
 
-.agent-preview-markdown h1 { font-size: 19px; }
+.agent-preview-markdown h1 { font-size: 18px; }
 .agent-preview-markdown h2 { font-size: 17px; }
-.agent-preview-markdown h3,
+.agent-preview-markdown h3 { font-size: 16px; }
 .agent-preview-markdown h4 { font-size: 15px; }
+.agent-preview-markdown h5,
+.agent-preview-markdown h6 { font-size: 14px; }
 
 .agent-preview-markdown ul,
 .agent-preview-markdown ol {
-  margin: 8px 0 10px;
-  padding-left: 22px;
+  margin: 6px 0 8px;
+  padding-left: 21px;
 }
 
-.agent-preview-markdown li + li { margin-top: 5px; }
+.agent-preview-markdown li + li { margin-top: 3px; }
 .agent-preview-markdown strong { color: #1f352e; font-weight: 700; }
 
 .agent-preview-markdown blockquote {
-  margin: 10px 0;
+  margin: 8px 0;
   padding: 7px 10px;
   border-left: 3px solid #8cc7b6;
   background: #eef7f4;
@@ -1464,6 +1469,12 @@ textarea {
 
 .agent-preview-markdown a { color: #0f735d; font-weight: 700; }
 
+.agent-preview-markdown hr {
+  margin: 12px 0;
+  border: 0;
+  border-top: 1px solid #dbe7e3;
+}
+
 .agent-preview-generation-state {
   display: flex;
   align-items: center;
diff --git a/ai_knowledge_base_v2/apps/user-client/src/components/ChatMessage.vue b/ai_knowledge_base_v2/apps/user-client/src/components/ChatMessage.vue
index f986afc..7e8dd84 100644
--- a/ai_knowledge_base_v2/apps/user-client/src/components/ChatMessage.vue
+++ b/ai_knowledge_base_v2/apps/user-client/src/components/ChatMessage.vue
@@ -23,9 +23,17 @@ const reasoning = computed(() => props.reasoning || parsed.value.reasoning);
 const hasAnswer = computed(() => answer.value.trim().length > 0);
 const renderedContent = computed(() => {
   if (props.role !== "assistant") return answer.value;
-  return hasAnswer.value ? markdown.render(answer.value) : "";
+  return hasAnswer.value ? markdown.render(normalizeStandaloneHeadings(answer.value)) : "";
 });
 
+function normalizeStandaloneHeadings(content: string) {
+  return content.replace(/^([ \t]*)\*\*(.+)\*\*[ \t]*$/gm, (line, indent: string, title: string) => {
+    const normalizedTitle = title.trim();
+    if (!normalizedTitle || normalizedTitle.length > 48 || normalizedTitle.includes("**")) return line;
+    return `${indent}### ${normalizedTitle}`;
+  });
+}
+
 function splitReasoning(content: string) {
   const lower = content.toLowerCase();
   let answer = "";
diff --git a/ai_knowledge_base_v2/apps/user-client/src/styles.css b/ai_knowledge_base_v2/apps/user-client/src/styles.css
index 86b69ad..32a01b3 100644
--- a/ai_knowledge_base_v2/apps/user-client/src/styles.css
+++ b/ai_knowledge_base_v2/apps/user-client/src/styles.css
@@ -1321,7 +1321,7 @@ textarea:focus-visible {
   white-space: pre-wrap;
   color: inherit;
   font-size: 15px;
-  line-height: 1.78;
+  line-height: 1.7;
   letter-spacing: 0;
 }
 
@@ -1369,35 +1369,39 @@ textarea:focus-visible {
 
 .markdown-content > :first-child { margin-top: 0; }
 .markdown-content > :last-child { margin-bottom: 0; }
-.markdown-content p { margin: 0 0 12px; }
+.markdown-content p { margin: 0 0 8px; }
 
 .markdown-content h1,
 .markdown-content h2,
 .markdown-content h3,
-.markdown-content h4 {
-  margin: 20px 0 9px;
+.markdown-content h4,
+.markdown-content h5,
+.markdown-content h6 {
+  margin: 15px 0 6px;
   color: var(--chat-text);
-  line-height: 1.45;
+  line-height: 1.42;
   font-weight: 700;
 }
 
 .markdown-content h1 { font-size: 20px; }
 .markdown-content h2 { font-size: 18px; }
-.markdown-content h3,
+.markdown-content h3 { font-size: 17px; }
 .markdown-content h4 { font-size: 16px; }
+.markdown-content h5,
+.markdown-content h6 { font-size: 15px; }
 
 .markdown-content ul,
 .markdown-content ol {
-  margin: 8px 0 13px;
-  padding-left: 22px;
+  margin: 6px 0 9px;
+  padding-left: 21px;
 }
 
-.markdown-content li + li { margin-top: 6px; }
+.markdown-content li + li { margin-top: 3px; }
 .markdown-content strong { color: var(--chat-text); font-weight: 700; }
 
 .markdown-content blockquote {
-  margin: 12px 0;
-  padding: 8px 12px;
+  margin: 9px 0;
+  padding: 7px 11px;
   border-left: 3px solid #8cc7b6;
   background: var(--chat-brand-soft);
   color: #526b63;
@@ -1405,6 +1409,12 @@ textarea:focus-visible {
 
 .markdown-content blockquote p { margin: 0; }
 
+.markdown-content hr {
+  margin: 14px 0;
+  border: 0;
+  border-top: 1px solid var(--chat-border);
+}
+
 .chat-composer {
   position: relative;
   z-index: 6;
diff --git a/ai_knowledge_base_v2/design-qa.md b/ai_knowledge_base_v2/design-qa.md
index e98ad77..eee85f4 100644
--- a/ai_knowledge_base_v2/design-qa.md
+++ b/ai_knowledge_base_v2/design-qa.md
@@ -51,6 +51,41 @@ final result: passed
 
 ---
 
+# Markdown 长回答排版修复验收（2026-07-17）
+
+## 对照范围
+
+- 问题截图：`/var/folders/hn/vg5lxj0j60d2cp0k6vv_k0mw0000gn/T/codex-clipboard-dc66a8a3-c423-4661-b29a-9c917754b888.png`
+- 修复后完整页面：`test_records/screenshots/Markdown排版_修复后.png`
+- 视口：1135 × 874，用户端 430px 固定聊天容器。
+- 状态：真实历史消息接口，包含 H1、H2、独立加粗小标题、正文、列表和引用块。
+
+## 比较历史
+
+- [P1] 修复前：模型常用的独立 `**加粗文本**` 只显示为加粗正文，没有标题字号和上下间距层级。
+- [P1] 修复前：正文行高、段落底部间距、列表条目间距和引用块上下间距叠加，长回答出现过大断层。
+- 修复：独立且不超过 48 字的加粗行按 H3 小标题渲染；普通行内加粗保持原语义。
+- 修复：用户端与后台预览统一收紧段落、列表、引用和标题间距，并补齐 H5、H6 和分隔线样式。
+
+## 必查视觉面
+
+- 字体与排版：用户端实测 H1/H2/H3/正文为 20/18/17/15px，标题层级清楚；正文行高 25.5px。
+- 间距与布局：标题上下间距为 15/6px，段落底部 8px，列表条目 3px，引用块顶部 9px；没有大块空白或水平溢出。
+- 颜色与令牌：继续使用现有深墨绿正文、雾绿引用背景和边框令牌，未引入新色系。
+- 图像与资源：本次为文本排版修复，无新增图像、图标或外部资源。
+- 文案与内容：Markdown 原文未被更改，只在展示层识别独立加粗小标题。
+
+## 交互与工程检查
+
+- DOM 实测确认独立加粗行已渲染为 H3，H1、H2、列表和引用均为正确语义节点。
+- 完整视图已能清晰判断字号、间距、列表和引用块，无需额外放大局部截图。
+- 用户端与后台预览 `npm run build`：通过。
+- 未发现剩余 P0、P1、P2 级问题。
+
+final result: passed
+
+---
+
 # 后台登录页视觉重构验收（2026-07-13）
 
 ## 对照范围
diff --git a/ai_knowledge_base_v2/test_records/screenshots/Markdown排版_修复后.png b/ai_knowledge_base_v2/test_records/screenshots/Markdown排版_修复后.png
new file mode 100644
index 0000000..7b4f29d
Binary files /dev/null and b/ai_knowledge_base_v2/test_records/screenshots/Markdown排版_修复后.png differ