Generally, information security of smart grid include physical security, cyber security, data security, backups and recovery. This paper focus on user data security and the existed problems, add our thoughts where we need to be in smart grid. Furthermore, the conception and the operating mechanism of smart grid are elaborated in the paper. This paper propose identity authentication and security domain to ensure the safety of the cyber security for smart grid. Use authentication to prevent unauthorized users access, make use of automated risk assessment tool to divide security domain, isolate information risk. Finally it reaches a conclusion that the popularization of smart grid should emphasis on the user security of information exchange.