As the security specifications for IEC 61850 P2P communication protocol（real-time communication）， IEC 62351-6 recommends the adoption of authentication for ensuring the safety of data transmission. To meet the requirement for the data flow and data security objectives in IEC 61850 digital substations， a method of implementing identity authentication with extended safe message through SHA-1 and DES encryption is put forward. Through the security analysis， it can meet the confidentiality，integrity and validity of the message. Further， by taking the bus fault on the unified star and the ring network in the whole D2-1 substation as an example， the OPNET network simulation and calculation are applied to the process of authentication. It is proved that the substation communication program has both good security and real-time character.