diff --git a/datetime/datetime.go b/datetime/datetime.go
index 5a23954..d3a24a5 100644
--- a/datetime/datetime.go
+++ b/datetime/datetime.go
@@ -124,19 +124,35 @@ func GetNightTimestamp() int64 {
 
 // FormatTimeToStr convert time to string.
 // Play: https://go.dev/play/p/_Ia7M8H_OvE
-func FormatTimeToStr(t time.Time, format string) string {
+func FormatTimeToStr(t time.Time, format string, timezone ...string) string {
+	if timezone != nil && timezone[0] != "" {
+		loc, err := time.LoadLocation(timezone[0])
+		if err != nil {
+			return ""
+		}
+		return t.In(loc).Format(timeFormat[format])
+	}
 	return t.Format(timeFormat[format])
 }
 
 // FormatStrToTime convert string to time.
 // Play: https://go.dev/play/p/1h9FwdU8ql4
-func FormatStrToTime(str, format string) (time.Time, error) {
-	v, ok := timeFormat[format]
+func FormatStrToTime(str, format string, timezone ...string) (time.Time, error) {
+	tf, ok := timeFormat[format]
 	if !ok {
 		return time.Time{}, fmt.Errorf("format %s not found", format)
 	}
 
-	return time.Parse(v, str)
+	if timezone != nil && timezone[0] != "" {
+		loc, err := time.LoadLocation(timezone[0])
+		if err != nil {
+			return time.Time{}, err
+		}
+
+		return time.ParseInLocation(tf, str, loc)
+	}
+
+	return time.Parse(tf, str)
 }
 
 // BeginOfMinute return beginning minute time of day.
diff --git a/datetime/datetime_test.go b/datetime/datetime_test.go
index 803c177..ebedfa9 100644
--- a/datetime/datetime_test.go
+++ b/datetime/datetime_test.go
@@ -147,6 +147,9 @@ func TestFormatTimeToStr(t *testing.T) {
 		actual := FormatTimeToStr(datetime, cases[i])
 		assert.Equal(expected[i], actual)
 	}
+
+	ds := FormatTimeToStr(datetime, "yyyy-mm-dd hh:mm:ss", "EST")
+	t.Log(ds)
 }
 
 func TestFormatStrToTime(t *testing.T) {
@@ -163,19 +166,23 @@ func TestFormatStrToTime(t *testing.T) {
 		"dd-mm-yy hh:mm:ss", "yyyy/mm/dd hh:mm:ss",
 		"yyyy/mm"}
 
-	datetimeStr := []string{
+	expected := []string{
 		"2021-01-02 16:04:08", "2021-01-02",
 		"02-01-21 16:04:08", "2021/01/02 16:04:08",
 		"2021/01"}
 
 	for i := 0; i < len(cases); i++ {
-		actual, err := FormatStrToTime(datetimeStr[i], cases[i])
+		actual, err := FormatStrToTime(expected[i], cases[i])
 		if err != nil {
 			t.Fatal(err)
 		}
-		expected, _ := time.Parse(formats[i], datetimeStr[i])
+		expected, _ := time.Parse(formats[i], expected[i])
 		assert.Equal(expected, actual)
 	}
+
+	estTime, err := FormatStrToTime("2021-01-02 16:04:08", "yyyy-mm-dd hh:mm:ss", "EST")
+	t.Log(estTime)
+	assert.IsNil(err)
 }
 
 func TestBeginOfMinute(t *testing.T) {
diff --git a/docs/datetime.md b/docs/datetime.md
index 6d29666..4f03994 100644
--- a/docs/datetime.md
+++ b/docs/datetime.md
@@ -838,7 +838,7 @@ func main() {
 <b>Signature:</b>
 
 ```go
-func FormatTimeToStr(t time.Time, format string) string
+func FormatTimeToStr(t time.Time, format string, timezone ...string) string
 ```
 
 <b>Example:</b>
@@ -877,7 +877,7 @@ func main() {
 <b>Signature:</b>
 
 ```go
-func FormatStrToTime(str, format string) (time.Time, error)
+func FormatStrToTime(str, format string, timezone ...string) (time.Time, error)
 ```
 
 <b>Example:</b>
diff --git a/docs/datetime_zh-CN.md b/docs/datetime_zh-CN.md
index e2572c6..1669d0e 100644
--- a/docs/datetime_zh-CN.md
+++ b/docs/datetime_zh-CN.md
@@ -838,7 +838,7 @@ func main() {
 <b>函数签名:</b>
 
 ```go
-func FormatTimeToStr(t time.Time, format string) string
+func FormatTimeToStr(t time.Time, format string, timezone ...string) string
 ```
 
 <b>示例:</b>
@@ -877,7 +877,7 @@ func main() {
 <b>函数签名:</b>
 
 ```go
-func FormatStrToTime(str, format string) (time.Time, error)
+func FormatStrToTime(str, format string, timezone ...string) (time.Time, error)
 ```
 
 <b>示例:</b>