E-government extranet is a window to display the image of the government, service people. Its purpose is resource sharing, efficient convenience, the security is particularly important. In this paper, in order to solve the security problem of e-government extranet, we put forward the design scheme of security system. Analysis shows that, by applying cryptographic service, unified user management, unified identity authentication, unified resource and authorization management and a series of safety measures can effectively guarantee the safety and reliability of e-government extranet.