The text aim the currently unsafe transport situation of the symmetric key of symmetric encryption algorithm, presenting the improved key generation algorithm based on the initial keys and key synthesis function matrix.premising the key transmission security effectively without sacrificing computing speed. Finally, the text illustrates the implementation model and implementation process of this improvement dynamic generated symmetric of symmetric key by an example. The text study conclusion is this improved symmetric key dynamic generation algorithm principle is simple, efficiency is high, suitable for the field of encryption research and extension for further use.