The present invention provides a fast handoff method in a wireless Local Area Network, the method is that a line mobile node STA selects an Access Point aggregation of the Wireless Local Area Network swept the frequency; the STA performs the interaction of the unicast type detecting and authenticating information to the AP aggregation, completes an active frequency sweep process, and selects a goal AP; the STA and the goal AP are associated newly. The present invention also provides a fast handoff method by adopting the unicast type active sweep-frequency and augmenting the safety during the two stages of the re-authentication. A technical proposal provided by the present invention merges the two stages of the sweep-frequency and the re-authentication into one sweep-frequency authentication stage, and the unicast type active sweep-frequency method is also adopted, to effectively decrease the waiting time consumed in a channel and reduce the handover time delay; a Message Integrity Identifying Code is joined during the interaction of the sweep-frequency authentication information, to enhance the safety of the switch. The other technical proposal also decreases the waiting time consumed in the channel, decreases the handover time delay, and enhances the safety of the switch.