Method for access control, access gateway and authentication server

The invention discloses a method for controlling access, an access gateway and an authentication server which belongs to the communications technology field. The method includes steps as follows: when a terminal accesses 3GPP network from non-3GPP network, judging the terminal whether having multi-module ability and switching ability for signed up various type network, and the network type corresponding to the multi-module ability includes at two network types corresponding to one switching ability of the switching ability; if yes, the access gateway in non 3GPP network obtains PDN GW address; if no, no-obtain PDN GW address. The access gateway includes a sending module and a receiving module. The authentication server includes a receiving module and a sending module. The method can realize that the terminal probable occurring network switch is anchored on PDN GW, the terminal no-probable occurring network switch is not anchored when the terminal accesses 3GPP network from non 3GPP for avoiding unnecessary burthen to PDN GW.