diff --git a/res/doc/sample_en.yaml b/res/doc/sample_en.yaml
index 0fec0aeb7a39400ce3668bd54a723dedc5a94099..94a9610f38e36881df532e4256b62ff94db4b3e5 100644
--- a/res/doc/sample_en.yaml
+++ b/res/doc/sample_en.yaml
@@ -52,7 +52,7 @@ desc:
     # Intervals can be set as random by R, e.g. range: 1-10:R. Set either random or a specified step.
     # Use a file to specify a list, e.g. range: list.txt. If the file name is a relative path, it is based on the config file.
     # Use {n} to repeat a element, e.g. range: user1{100},user2{100}.
-    # Use [], if intervals and elements are repeated, e.g. range: [user1,user2,user3]{100}.
+    # Use [], if intervals and elements are repeated, e.g. range: [user1,user2,user3]{100}, [1-100]{10}.
 
 author: zentao
 version: 1.0
@@ -83,14 +83,19 @@ fields:
     postfix: "\t"
 
   - field: field_repeat                 # Use {} to define repeated elements.
-    range: user-1{3},[user2,user3]{2}   # user-1,user-1,user-1,user2,user3,user2,user3
+    range: u-1{3},[u2,u3]{2},[1-3]{3}   # u-1,u-1,u-1,u2,u2,user3,user3,1,1,1,2,2,2,3,3,3
     postfix: "\t"
 
   - field: field_format                 # Output as formatted strings.
     range: 1-10                         # passwd 1,passwd 2,passwd 3 ... passwd10。
     format: "passwd%02d"
     postfix: "\t"
-
+  
+  - field: field_length                 # Fixed length field.
+    range: 1-100                        # 001,002,003..., 099,100
+    length: 3                           # the length in Byte.
+    leftpad: 0                          # Using 0 to pad.
+  
   - field: field_use_another_file       # Other definition file can be referred.
     config: number_field.yaml           # Refer to the definition in number_field.yaml of the current directory.
     postfix: "\t"