A load balancing method for a wireless communication system, which has a backbone network, more than one Access Point connected to the backbone network and more than one client. In the method, the client transmits a Probe Request message to the more than one Access Point; the Access Point monitors its load. If the Access Point is under an overload situation, it transmits a Probe Response message to the client by the minimum transmitting power. If the Access Point is under normal load situation, it transmits a Probe Response message to the client by normal transmitting power. The client preferentially chooses the Access Point under normal load situation to access based on the signal strength of the received Probe Respond message. The method thus provides the client with a priority of the Access Points, wherein the Access Point under an overload situation has a lower priority.