In this paper , the production , development , principle and configuration of the SIMATIC S7-200PLC are introduced , through the introduction Encryption and Decipher method are further analyzed and researched . Then feasible method of Encryption which apply to software , program and logic circuit is suggested . Besides , the popular method of Encryption which dissolves the SIMATIC S7-200PLC is discussed .More , Decipher method is researched , simple method of program and logic circuit are advised .