diff --git a/conversation/store.go b/conversation/store.go
index a5162a4..874265d 100644
--- a/conversation/store.go
+++ b/conversation/store.go
@@ -30,11 +30,16 @@ func (s *Store) path(id string) string {
 }
 
 func (s *Store) Create() (*message.Conversation, error) {
+	return s.CreateWithPreset("")
+}
+
+func (s *Store) CreateWithPreset(preset string) (*message.Conversation, error) {
 	conv := &message.Conversation{
-		ID:        utils.NewUUID(),
-		Title:     "新对话",
-		CreatedAt: time.Now(),
-		UpdatedAt: time.Now(),
+		ID:           utils.NewUUID(),
+		Title:        "新对话",
+		CreatedAt:    time.Now(),
+		UpdatedAt:    time.Now(),
+		PresetPrompt: strings.TrimSpace(preset),
 	}
 	if err := s.Save(conv); err != nil {
 		return nil, err
@@ -124,7 +129,7 @@ func SaveMessages(store *Store, id string, messages []message.ChatMessage, assis
 	if err != nil {
 		return err
 	}
-	conv.Messages = append([]message.ChatMessage(nil), messages...)
+	conv.Messages = filterPresetMessages(messages)
 	conv.Messages = append(conv.Messages, message.ChatMessage{Role: "assistant", Content: assistantContent})
 	if conv.Title == "" || conv.Title == "新对话" {
 		conv.Title = GenTitle(conv.Messages)
@@ -132,6 +137,17 @@ func SaveMessages(store *Store, id string, messages []message.ChatMessage, assis
 	return store.Save(conv)
 }
 
+func filterPresetMessages(messages []message.ChatMessage) []message.ChatMessage {
+	filtered := make([]message.ChatMessage, 0, len(messages))
+	for _, msg := range messages {
+		if msg.Hidden && strings.EqualFold(msg.Role, "system") {
+			continue
+		}
+		filtered = append(filtered, msg)
+	}
+	return filtered
+}
+
 func GenTitle(messages []message.ChatMessage) string {
 	for _, m := range messages {
 		if m.Hidden {
diff --git a/conversation/store_test.go b/conversation/store_test.go
new file mode 100644
index 0000000..23263d5
--- /dev/null
+++ b/conversation/store_test.go
@@ -0,0 +1,70 @@
+package conversation
+
+import (
+	"testing"
+
+	"aichat/message"
+)
+
+func TestCreateWithPresetSavesPresetPrompt(t *testing.T) {
+	store := NewStore(t.TempDir())
+	conv, err := store.CreateWithPreset("  你是测试助手  ")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if conv.PresetPrompt != "你是测试助手" {
+		t.Fatalf("preset_prompt = %q", conv.PresetPrompt)
+	}
+	loaded, err := store.Get(conv.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if loaded.PresetPrompt != "你是测试助手" {
+		t.Fatalf("loaded preset_prompt = %q", loaded.PresetPrompt)
+	}
+	if len(loaded.Messages) != 0 {
+		t.Fatalf("preset should not be stored in messages: %#v", loaded.Messages)
+	}
+}
+
+func TestCreateKeepsEmptyPresetPrompt(t *testing.T) {
+	store := NewStore(t.TempDir())
+	conv, err := store.Create()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if conv.PresetPrompt != "" {
+		t.Fatalf("preset_prompt = %q", conv.PresetPrompt)
+	}
+}
+
+func TestSaveMessagesKeepsPresetPromptAndFiltersPresetMessages(t *testing.T) {
+	store := NewStore(t.TempDir())
+	conv, err := store.CreateWithPreset("你是测试助手")
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = SaveMessages(store, conv.ID, []message.ChatMessage{
+		{Role: "system", Content: "你是测试助手", Hidden: true},
+		{Role: "user", Content: "你好"},
+	}, "你好，我在")
+	if err != nil {
+		t.Fatal(err)
+	}
+	loaded, err := store.Get(conv.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if loaded.PresetPrompt != "你是测试助手" {
+		t.Fatalf("preset_prompt = %q", loaded.PresetPrompt)
+	}
+	if len(loaded.Messages) != 2 {
+		t.Fatalf("messages length = %d: %#v", len(loaded.Messages), loaded.Messages)
+	}
+	if loaded.Messages[0].Role != "user" || loaded.Messages[0].Content != "你好" {
+		t.Fatalf("unexpected first message: %#v", loaded.Messages[0])
+	}
+	if loaded.Messages[1].Role != "assistant" || loaded.Messages[1].Content != "你好，我在" {
+		t.Fatalf("unexpected assistant message: %#v", loaded.Messages[1])
+	}
+}
diff --git a/message/types.go b/message/types.go
index 448bf38..bd50b8c 100644
--- a/message/types.go
+++ b/message/types.go
@@ -18,9 +18,10 @@ type ChatRequest struct {
 }
 
 type Conversation struct {
-	ID        string        `json:"id"`
-	Title     string        `json:"title"`
-	CreatedAt time.Time     `json:"created_at"`
-	UpdatedAt time.Time     `json:"updated_at"`
-	Messages  []ChatMessage `json:"messages,omitempty"`
+	ID           string        `json:"id"`
+	Title        string        `json:"title"`
+	CreatedAt    time.Time     `json:"created_at"`
+	UpdatedAt    time.Time     `json:"updated_at"`
+	PresetPrompt string        `json:"preset_prompt,omitempty"`
+	Messages     []ChatMessage `json:"messages,omitempty"`
 }
diff --git a/server/handlers.go b/server/handlers.go
index 1cbe74f..9be2bfc 100644
--- a/server/handlers.go
+++ b/server/handlers.go
@@ -26,6 +26,11 @@ type activeProfileRequest struct {
 	Name string `json:"name"`
 }
 
+type createConversationRequest struct {
+	Preset       string `json:"preset"`
+	PresetPrompt string `json:"preset_prompt"`
+}
+
 func (s *Server) indexHandler(c *gin.Context) {
 	profile := s.aiState.ActiveProfile()
 	c.HTML(http.StatusOK, "chat.html", gin.H{
@@ -89,7 +94,15 @@ func (s *Server) listConversationsHandler(c *gin.Context) {
 }
 
 func (s *Server) createConversationHandler(c *gin.Context) {
-	conv, err := s.store.Create()
+	var req createConversationRequest
+	if c.Request.Body != nil {
+		_ = c.ShouldBindJSON(&req)
+	}
+	preset := req.PresetPrompt
+	if strings.TrimSpace(preset) == "" {
+		preset = req.Preset
+	}
+	conv, err := s.store.CreateWithPreset(preset)
 	if err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "创建对话失败: " + err.Error()})
 		return
@@ -118,6 +131,41 @@ func (s *Server) deleteConversationHandler(c *gin.Context) {
 	c.Status(http.StatusNoContent)
 }
 
+func conversationPresetPrompt(store *conversation.Store, id string) string {
+	id = strings.TrimSpace(id)
+	if id == "" || store == nil {
+		return ""
+	}
+	conv, err := store.Get(id)
+	if err != nil {
+		return ""
+	}
+	return strings.TrimSpace(conv.PresetPrompt)
+}
+
+func conversationContextMessages(messages []message.ChatMessage, preset string) []message.ChatMessage {
+	preset = strings.TrimSpace(preset)
+	if preset == "" {
+		return append([]message.ChatMessage(nil), messages...)
+	}
+	cleaned := filterRequestPresetMessages(messages)
+	contextMessages := make([]message.ChatMessage, 0, len(cleaned)+1)
+	contextMessages = append(contextMessages, message.ChatMessage{Role: "system", Content: preset, Hidden: true})
+	contextMessages = append(contextMessages, cleaned...)
+	return contextMessages
+}
+
+func filterRequestPresetMessages(messages []message.ChatMessage) []message.ChatMessage {
+	filtered := make([]message.ChatMessage, 0, len(messages))
+	for _, msg := range messages {
+		if msg.Hidden && strings.EqualFold(msg.Role, "system") {
+			continue
+		}
+		filtered = append(filtered, msg)
+	}
+	return filtered
+}
+
 // chatHandler 流式 SSE 对话接口
 func (s *Server) chatHandler(c *gin.Context) {
 	var req message.ChatRequest
@@ -163,8 +211,8 @@ func (s *Server) chatHandler(c *gin.Context) {
 	usage := stream.NewTracker()
 	ctx = stream.ContextWithTracker(ctx, usage)
 
-	contextMessages := req.Messages
-	chatWindow := contextwindow.ApplyChatWindow(req.Messages, profile.Config.ContextWindowTokens)
+	contextMessages := conversationContextMessages(req.Messages, conversationPresetPrompt(s.store, req.ConversationID))
+	chatWindow := contextwindow.ApplyChatWindow(contextMessages, profile.Config.ContextWindowTokens)
 	if chatWindow.Removed > 0 || chatWindow.Overflow {
 		emitTrace("context_window", "chat", "success", "已清理对话历史上下文", map[string]any{"max_tokens": chatWindow.MaxTokens, "before_tokens": chatWindow.BeforeTokens, "after_tokens": chatWindow.AfterTokens, "removed_messages": chatWindow.Removed, "overflow": chatWindow.Overflow, "base_overflow": chatWindow.BaseOverflow})
 	}
diff --git a/templates/chat.html b/templates/chat.html
index e303392..8cf0f51 100644
--- a/templates/chat.html
+++ b/templates/chat.html
@@ -771,7 +771,12 @@ async function loadConversationList() {
 }
 
 async function createConversation() {
-  const res = await fetch('/api/conversations', { method: 'POST' });
+  const preset = getPresetPrompt();
+  const res = await fetch('/api/conversations', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ preset_prompt: preset }),
+  });
   if (!res.ok) {
     const err = await res.json().catch(() => ({ error: '创建对话失败' }));
     throw new Error(err.error || '创建对话失败');
@@ -1075,7 +1080,6 @@ async function sendMessage() {
 
   try {
     if (!currentConvId) {
-      ensurePresetLoaded();
       const conv = await createConversation();
       currentConvId = conv.id;
       await loadConversationList();