System and method for realizing single sign-on

The invention discloses a system and method for realizing single sign-on. The system comprises a portal server, a proxy service cluster and an application system, wherein the portal server is used for authenticating the identity of a user, and after passing the authentication, generating a user login note and transmitting the user login note to the proxy service cluster; the application system is used for authenticating the identity of the user, and after passing the authentication, transmitting a business request note to the proxy service cluster by the user through a client; the proxy service cluster is used for comparing the business request note with the user login note, and if the business request note is consistent with the user login note, then transmitting business data to the client by the application system. The system for realizing single sign-on provided by the invention solves the problems in the existing single sign-on process that the safe reliability of data transmission is lower and the workload of the portal server is higher.