A method and a system for establishing a tunnel in a wireless local area network (WLAN) are described. The method includes the following steps. A WLAN terminal initiates a tunnel establishment request in an Internet Key Exchange Security Association (IKE SA) that has been established. It is judged whether the number of tunnels already established in the IKE SA reaches a corresponding first threshold or not, if the number of tunnels does not reach the corresponding first threshold, establishing the tunnel for the WLAN terminal; otherwise, rejecting the establishment of the tunnel for the WALN terminal. It is decided whether to establish the tunnel for the WLAN terminal or not by judging whether the number of the tunnels already established in each IKE SA reaches the corresponding threshold or not during the tunnel establishment of the WLAN terminal, thereby effectively controlling the rationality and validity about the tunnel establishment.