Abstract：The electric energy meters conformed to the STS protocol have been applied in almost 100 countries. The relevant system standards have been transformed into IEC62055 series standards. IEC62055 series standards contain prepayment system, consumer information system, power selling system, Token, prepayment meters and the interfaces in the substance. This paper researches the systematic framework of IEC 62055 and analyzes Standard Transfer Specification(STS), STS standardized the practical equipment and code, and is used for the safety management(producing, storage, remedy and delivery) of the key in the power selling system. This paper mainly studies the encryption process and encryption algorithm of Token and the security of the vending electricity method of prepayment meters measurement and the key management system.