Authentication method, server, user equipment and communication system

The embodiment of the invention relates to an authentication method, a server, user equipment and a communication system. The authentication method comprises that: a home domain authentication server generates a home domain root key in the authentication process of accessing a first network by the user equipment, and authenticates a second network of the user equipment accessed into a home domain with the user equipment based on the home domain root key; and when authentication servers associated with the home domain authentication server comprise an access domain authentication server, the home domain authentication server generates an access domain root key for the access domain authentication server according to the home domain root key, and sends the access domain root key to the access domain authentication server for the access domain authentication server and the user equipment to authenticate the second network of the user equipment accessed into an access domain based on the access domain root key. The embodiment of the invention is favorable for improving the authentication efficiency when converged network is accessed by the user equipment, and provides realization possibility for realizing quick re-authentication or quick switch of the authentication server corresponding to each level to the user equipment.