diff --git a/backend/src/routes/department.routes.ts b/backend/src/routes/department.routes.ts
index c5aeb44..501af7c 100644
--- a/backend/src/routes/department.routes.ts
+++ b/backend/src/routes/department.routes.ts
@@ -21,6 +21,24 @@ const updateDeptSchema = createDeptSchema.partial()
 /** 获取部门树 */
 router.get('/', authMiddleware, async (req: AuthRequest, res, next) => {
   try {
+    // 兼容历史组织：若无任何部门，自动创建根部门（公司名）
+    const existing = await prisma.department.findFirst({ where: { orgId: req.user!.orgId! } })
+    if (!existing) {
+      const org = await prisma.organization.findUnique({ where: { id: req.user!.orgId! } })
+      if (org) {
+        await prisma.department.create({
+          data: {
+            orgId: org.id,
+            name: org.name,
+            parentId: null,
+            level: 0,
+            sortOrder: 0,
+            description: '组织根节点',
+            createdBy: req.user!.id,
+          },
+        })
+      }
+    }
     const departments = await prisma.department.findMany({
       where: { orgId: req.user!.orgId! },
       orderBy: [{ sortOrder: 'asc' }, { createdAt: 'asc' }],
@@ -37,7 +55,12 @@ router.post('/', authMiddleware, async (req: AuthRequest, res, next) => {
   try {
     const data = createDeptSchema.parse(req.body)
     // 空字符串视为无父部门，统一转为 null
-    const parentId = data.parentId && data.parentId.trim() !== '' ? data.parentId : null
+    let parentId = data.parentId && data.parentId.trim() !== '' ? data.parentId : null
+    // 若未指定父部门，默认挂到根部门（level=0）下
+    if (!parentId) {
+      const root = await prisma.department.findFirst({ where: { orgId: req.user!.orgId!, parentId: null }, orderBy: { sortOrder: 'asc' } })
+      if (root) parentId = root.id
+    }
     let level = 0
     if (parentId) {
       const parent = await prisma.department.findFirst({ where: { id: parentId, orgId: req.user!.orgId! } })
diff --git a/backend/src/services/auth.service.ts b/backend/src/services/auth.service.ts
index 378b363..a5bd8b5 100644
--- a/backend/src/services/auth.service.ts
+++ b/backend/src/services/auth.service.ts
@@ -27,6 +27,19 @@ export async function register(orgName: string, phone: string, password: string)
     },
   })
 
+  // 自动创建根部门（公司名），作为组织架构的顶层节点
+  await prisma.department.create({
+    data: {
+      orgId: org.id,
+      name: orgName,
+      parentId: null,
+      level: 0,
+      sortOrder: 0,
+      description: '组织根节点',
+      createdBy: user.id,
+    },
+  })
+
   await prisma.user.update({
     where: { id: user.id },
     data: { lastLoginAt: new Date() },
diff --git a/frontend/src/pages/OrgChart.tsx b/frontend/src/pages/OrgChart.tsx
index 0d748f7..f95043c 100644
--- a/frontend/src/pages/OrgChart.tsx
+++ b/frontend/src/pages/OrgChart.tsx
@@ -61,10 +61,13 @@ export default function OrgChart() {
   }
 
   const renderTree = (items: any[], parentId: string | null, level: number = 0) => {
-    return items.filter(d => d.parentId === parentId).map(d => (
+    return items.filter(d => d.parentId === parentId).map(d => {
+      // 根部门（level=0 且无父部门）为公司节点，不可编辑/删除
+      const isRoot = d.level === 0 && !d.parentId
+      return (
       <div key={d.id}>
         <div
-          className="flex items-center gap-2 py-2 px-3 hover:bg-gray-50 rounded-md"
+          className={`flex items-center gap-2 py-2 px-3 rounded-md ${isRoot ? 'bg-primary/5 font-medium' : 'hover:bg-gray-50'}`}
           style={{ marginLeft: level * 24 }}
         >
           {items.some(c => c.parentId === d.id) ? (
@@ -74,29 +77,35 @@ export default function OrgChart() {
           ) : (
             <span className="w-4" />
           )}
-          <Building2 className="w-4 h-4 text-primary" />
+          <Building2 className={`w-4 h-4 ${isRoot ? 'text-primary' : 'text-gray-400'}`} />
           <span className="flex-1 text-sm">{d.name}</span>
+          {isRoot && <span className="text-xs text-primary">公司</span>}
           <span className="text-xs text-gray-400">{d._count?.employees || 0}人</span>
-          <button
-            onClick={() => {
-              setEditing(d)
-              setForm({ name: d.name, parentId: d.parentId || '', sortOrder: d.sortOrder, description: d.description || '' })
-              setShowModal(true)
-            }}
-            className="text-gray-400 hover:text-primary"
-          >
-            <Edit className="w-3.5 h-3.5" />
-          </button>
-          <button
-            onClick={() => { if (confirm(`确认删除部门"${d.name}"？`)) deleteMutation.mutate(d.id) }}
-            className="text-gray-400 hover:text-danger"
-          >
-            <Trash2 className="w-3.5 h-3.5" />
-          </button>
+          {!isRoot && (
+            <>
+              <button
+                onClick={() => {
+                  setEditing(d)
+                  setForm({ name: d.name, parentId: d.parentId || '', sortOrder: d.sortOrder, description: d.description || '' })
+                  setShowModal(true)
+                }}
+                className="text-gray-400 hover:text-primary"
+              >
+                <Edit className="w-3.5 h-3.5" />
+              </button>
+              <button
+                onClick={() => { if (confirm(`确认删除部门"${d.name}"？`)) deleteMutation.mutate(d.id) }}
+                className="text-gray-400 hover:text-danger"
+              >
+                <Trash2 className="w-3.5 h-3.5" />
+              </button>
+            </>
+          )}
         </div>
         {expanded.has(d.id) && renderTree(items, d.id, level + 1)}
       </div>
-    ))
+      )
+    })
   }
 
   return (
@@ -130,7 +139,9 @@ export default function OrgChart() {
             <span className="text-sm font-medium">部门列表</span>
             <Button size="sm" onClick={() => {
               setEditing(null)
-              setForm({ name: '', parentId: '', sortOrder: 0, description: '' })
+              // 默认父部门为根部门（level=0 且 parentId=null）
+              const root = departments.find((d: any) => d.level === 0 && !d.parentId)
+              setForm({ name: '', parentId: root?.id || '', sortOrder: 0, description: '' })
               setShowModal(true)
             }}>
               <Plus className="w-4 h-4 mr-1" />新增部门
@@ -158,9 +169,10 @@ export default function OrgChart() {
             <div>
               <Label>上级部门</Label>
               <Select value={form.parentId} onChange={(e) => setForm({ ...form, parentId: e.target.value })}>
-                <option value="">无（根部门）</option>
                 {departments.filter((d: any) => d.id !== editing?.id).map((d: any) => (
-                  <option key={d.id} value={d.id}>{d.name}</option>
+                  <option key={d.id} value={d.id}>
+                    {d.level === 0 && !d.parentId ? `${d.name}（公司）` : d.name}
+                  </option>
                 ))}
               </Select>
             </div>