diff --git a/middleware/logger.go b/middleware/logger.go
index 07b68c3..52ba978 100644
--- a/middleware/logger.go
+++ b/middleware/logger.go
@@ -88,9 +88,11 @@ type (
 	OnLog func(string, *elton.Context)
 	// LoggerConfig logger config
 	LoggerConfig struct {
-		Format  string
-		OnLog   OnLog
-		Skipper elton.Skipper
+		// DefaultFill default fill for empty value
+		DefaultFill string
+		Format      string
+		OnLog       OnLog
+		Skipper     elton.Skipper
 	}
 )
 
@@ -191,7 +193,7 @@ func parseLoggerTags(desc []byte) []*LoggerTag {
 }
 
 // formatLog 格式化访问日志信息
-func formatLog(c *elton.Context, tags []*LoggerTag, startedAt time.Time) string {
+func formatLog(c *elton.Context, tags []*LoggerTag, startedAt time.Time, defaultFill string) string {
 	fn := func(tag *LoggerTag) string {
 		switch tag.category {
 		case host:
@@ -277,19 +279,15 @@ func formatLog(c *elton.Context, tags []*LoggerTag, startedAt time.Time) string
 
 	arr := make([]string, 0, len(tags))
 	for _, tag := range tags {
-		arr = append(arr, fn(tag))
+		v := fn(tag)
+		if v == "" {
+			v = defaultFill
+		}
+		arr = append(arr, v)
 	}
 	return strings.Join(arr, "")
 }
 
-// GenerateLog generate log function
-func GenerateLog(layout string) func(*elton.Context, time.Time) string {
-	tags := parseLoggerTags([]byte(layout))
-	return func(c *elton.Context, startedAt time.Time) string {
-		return formatLog(c, tags, startedAt)
-	}
-}
-
 // New create a logger middleware
 func NewLogger(config LoggerConfig) elton.Handler {
 	if config.Format == "" {
@@ -309,7 +307,7 @@ func NewLogger(config LoggerConfig) elton.Handler {
 		}
 		startedAt := time.Now()
 		err = c.Next()
-		str := formatLog(c, tags, startedAt)
+		str := formatLog(c, tags, startedAt, config.DefaultFill)
 		config.OnLog(str, c)
 		return err
 	}
diff --git a/middleware/logger_test.go b/middleware/logger_test.go
index a5cdef4..894af80 100644
--- a/middleware/logger_test.go
+++ b/middleware/logger_test.go
@@ -47,11 +47,10 @@ func TestLogger(t *testing.T) {
 	assert := assert.New(t)
 	t.Run("normal", func(t *testing.T) {
 		config := LoggerConfig{
-			Format: "{host} {remote} {real-ip} {method} {path} {proto} {query} {scheme} {uri} {referer} {userAgent} {size} {size-human} {status} {payload-size} {payload-size-human}",
+			DefaultFill: "-",
+			Format:      "{host} {remote} {real-ip} {method} {path} {proto} {query} {scheme} {uri} {referer} {userAgent} {size} {size-human} {status} {payload-size} {payload-size-human} {<x-empty}",
 			OnLog: func(log string, _ *elton.Context) {
-				if log != "aslant.site 192.0.2.1:1234 192.0.2.1 GET / HTTP/1.1 a=1&b=2 HTTPS https://aslant.site/?a=1&b=2 https://aslant.site/ test-agent 13 13B 200 12 12B" {
-					t.Fatalf("log format fail")
-				}
+				assert.Equal("aslant.site 192.0.2.1:1234 192.0.2.1 GET / HTTP/1.1 a=1&b=2 HTTPS https://aslant.site/?a=1&b=2 https://aslant.site/ test-agent 13 13B 200 12 12B -", log)
 			},
 		}
 		m := NewLogger(config)
@@ -166,19 +165,4 @@ func TestLogger(t *testing.T) {
 		assert.Nil(err)
 	})
 
-	t.Run("get log function", func(t *testing.T) {
-		layout := "{host} {remote} {real-ip} {method} {path} {proto} {query} {scheme} {uri} {referer} {userAgent} {size} {size-human} {status} {payload-size} {payload-size-human}"
-		fn := GenerateLog(layout)
-		req := httptest.NewRequest("GET", "https://aslant.site/?a=1&b=2", nil)
-		req.Header.Set("Referer", "https://aslant.site/")
-		req.Header.Set("User-Agent", "test-agent")
-		resp := httptest.NewRecorder()
-		c := elton.NewContext(resp, req)
-		c.BodyBuffer = bytes.NewBufferString("response-body")
-		c.RequestBody = []byte("request-body")
-		c.StatusCode = 200
-		startedAt := time.Now()
-		assert.Equal("aslant.site 192.0.2.1:1234 192.0.2.1 GET / HTTP/1.1 a=1&b=2 HTTPS https://aslant.site/?a=1&b=2 https://aslant.site/ test-agent 13 13B 200 12 12B", fn(c, startedAt))
-	})
-
 }