diff --git a/Cargo.toml b/Cargo.toml
index 52d0701..56d5ac7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "fastdate"
-version = "0.3.25"
+version = "0.3.26"
 edition = "2021"
 description = "Rust fast date carte"
 readme = "Readme.md"
diff --git a/benches/bench.rs b/benches/bench.rs
index fb5216a..fa55c75 100644
--- a/benches/bench.rs
+++ b/benches/bench.rs
@@ -138,3 +138,13 @@ fn bench_from_timestamp_millis(b: &mut Bencher) {
         });
     });
 }
+
+#[bench]
+fn bench_format(b: &mut Bencher) {
+    let dt=DateTime::from_str("1997-12-13T11:12:13.123456+09:00").unwrap();
+    b.iter(|| {
+        std::hint::black_box({
+            dt.format("YYYY-MM-DD/hh/mm/ss.000000");
+        });
+    });
+}
\ No newline at end of file
diff --git a/src/datetime.rs b/src/datetime.rs
index e87a40f..691b197 100644
--- a/src/datetime.rs
+++ b/src/datetime.rs
@@ -162,26 +162,64 @@ impl DateTime {
     ///
     /// ```
     pub fn format(&self, fmt: &str) -> String {
+        use std::fmt::Write;
         let (mut h, mut m, _) = self.offset_hms();
         let offset = self.offset();
-        let add_sub;
-        if offset > 0 {
-            add_sub = '+';
-        } else {
-            add_sub = '-';
-            h = h.abs();
-            m = m.abs();
+        let add_sub = if offset >= 0 { '+' } else { '-' };
+        let mut result = String::with_capacity(fmt.len());
+        let mut chars = fmt.chars();
+        while let Some(c) = chars.next() {
+            result.push(c);
+            if result.ends_with(".000000000") {
+                for _ in 0..".000000000".len() {
+                    result.pop();
+                }
+                write!(result, ".{:09}", self.nano()).unwrap()
+            } else if result.ends_with(".000000") {
+                for _ in 0..".000000".len() {
+                    result.pop();
+                }
+                write!(result, ".{:06}", self.nano() / 1000).unwrap()
+            } else if result.ends_with("+00:00") {
+                for _ in 0.."+00:00".len() {
+                    result.pop();
+                }
+                h = h.abs();
+                m = m.abs();
+                write!(result, "{}{:02}:{:02}", add_sub, h, m).unwrap();
+            } else if result.ends_with("YYYY") {
+                for _ in 0.."YYYY".len() {
+                    result.pop();
+                }
+                write!(result, "{:04}", self.year()).unwrap()
+            } else if result.ends_with("MM") {
+                for _ in 0.."MM".len() {
+                    result.pop();
+                }
+                result.write_fmt(format_args!("{:02}", self.mon())).unwrap()
+            } else if result.ends_with("DD") {
+                for _ in 0.."DD".len() {
+                    result.pop();
+                }
+                write!(result, "{:02}", self.day()).unwrap()
+            } else if result.ends_with("hh") {
+                for _ in 0.."hh".len() {
+                    result.pop();
+                }
+                write!(result, "{:02}", self.hour()).unwrap()
+            } else if result.ends_with("mm") {
+                for _ in 0.."mm".len() {
+                    result.pop();
+                }
+                write!(result, "{:02}", self.minute()).unwrap();
+            } else if result.ends_with("ss") {
+                for _ in 0.."ss".len() {
+                    result.pop();
+                }
+                write!(result, "{:02}", self.sec()).unwrap();
+            }
         }
-        fmt.replacen("YYYY", &self.year().to_string(), 1)
-            .replacen("MM", &self.mon().to_string(), 1)
-            .replacen("DD", &self.day().to_string(), 1)
-            .replacen("hh", &self.hour().to_string(), 1)
-            .replacen("mm", &self.minute().to_string(), 1)
-            .replacen("ss", &self.sec().to_string(), 1)
-            .replacen(".000000000", &format!(".{:09}", self.nano()), 1)
-            .replacen(".000000", &format!(".{:06}", self.micro()), 1)
-            .replacen("+00:00", &format!("{}{:02}:{:02}", add_sub, h, m), 1)
-            .to_string()
+        result
     }
 
     /// parse an string by format.
@@ -400,7 +438,7 @@ impl DateTime {
         Self {
             inner: time1::OffsetDateTime::from(s),
         }
-        .set_offset(offset)
+            .set_offset(offset)
     }
 
     /// stand "0000-00-00 00:00:00.000000000"
@@ -611,7 +649,7 @@ impl From<Date> for DateTime {
             "{:04}-{:02}-{:02} 00:00:00.000000000Z",
             arg.year, arg.mon, arg.day
         ))
-        .unwrap()
+            .unwrap()
     }
 }
 
@@ -630,7 +668,7 @@ impl From<Time> for DateTime {
             "0000-01-01 {:02}:{:02}:{:02}.{:09}Z",
             arg.hour, arg.minute, arg.sec, arg.nano
         ))
-        .unwrap()
+            .unwrap()
     }
 }
 
@@ -640,7 +678,7 @@ impl From<(Date, Time)> for DateTime {
             "{:04}-{:02}-{:02} {:02}:{:02}:{:02}.{:09}Z",
             arg.0.year, arg.0.mon, arg.0.day, arg.1.hour, arg.1.minute, arg.1.sec, arg.1.nano
         ))
-        .unwrap()
+            .unwrap()
     }
 }
 
@@ -651,7 +689,7 @@ impl From<(Date, Time, i32)> for DateTime {
             "{:04}-{:02}-{:02} {:02}:{:02}:{:02}.{:09}Z",
             arg.0.year, arg.0.mon, arg.0.day, arg.1.hour, arg.1.minute, arg.1.sec, arg.1.nano
         ))
-        .unwrap();
+            .unwrap();
         datetime = datetime.set_offset(arg.2).add_sub_sec(-arg.2 as i64);
         datetime
     }
@@ -694,8 +732,8 @@ impl PartialOrd for DateTime {
 
 impl Serialize for DateTime {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        S: Serializer,
+        where
+            S: Serializer,
     {
         serializer.serialize_str(&self.to_string())
     }
@@ -704,8 +742,8 @@ impl Serialize for DateTime {
 #[cfg(not(tarpaulin_include))]
 impl<'de> Deserialize<'de> for DateTime {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>,
+        where
+            D: Deserializer<'de>,
     {
         use serde::de::Error;
         let s = String::deserialize(deserializer)?;
diff --git a/tests/datetime.rs b/tests/datetime.rs
index be28517..040481b 100644
--- a/tests/datetime.rs
+++ b/tests/datetime.rs
@@ -870,9 +870,9 @@ fn test_format() {
         },
     ));
     let f = dt.format("YYYY-MM-DD/hh/mm/ss.000000");
-    assert_eq!(f, "2000-1-1/1/1/11.123456");
+    assert_eq!(f, "2000-01-01/01/01/11.123456");
     let f = dt.format("YYYY-MM-DD/hh/mm/ss.000000000");
-    assert_eq!(f, "2000-1-1/1/1/11.123456000");
+    assert_eq!(f, "2000-01-01/01/01/11.123456000");
 }
 
 #[test]
@@ -893,7 +893,7 @@ fn test_format2() {
     .set_offset(8 * 60 * 60);
     println!("dt={}", dt.to_string());
     let f = dt.format("YYYY-MM-DD/hh/mm/ss.000000/+00:00");
-    assert_eq!(f, "2000-1-1/9/1/11.123456/+08:00");
+    assert_eq!(f, "2000-01-01/09/01/11.123456/+08:00");
 }
 
 #[test]
@@ -914,7 +914,7 @@ fn test_format3() {
     .set_offset(-8 * 60 * 60);
     println!("dt={}", dt.to_string());
     let f = dt.format("YYYY-MM-DD/hh/mm/ss.000000/+00:00");
-    assert_eq!(f, "1999-12-31/17/1/11.123456/-08:00");
+    assert_eq!(f, "1999-12-31/17/01/11.123456/-08:00");
 }
 
 #[test]