Abstract: Several key problems of message encoding and decoding in C4ISR system simulation are analyzed，and new methods are put out.The detail design methods of storing rules of message encoding and decoding，data structure and function of encoding and decoding are brought out.And it also gives flow charts of message encoding and decoding.A novel method is designed to solve the problems of encoding and decoding in C4ISR system simulation，such as large number of messages and diverse encoding and decoding styles.And it is compared with the normal methods，so its advantage and disadvantage can be clearly shown.Rules of message encoding and decoding are stored in XML.Data structure and function of encoding and decoding are described through C++.The data flow drawing and main flow chart of program are given from the aspect of software engineering.Simulation results show that the design method of message encoding and decoding function is very novel，efficient and extensible.