A method, a device, and a system for acquiring application information in a WLAN are provided by embodiments of the present invention. A controller sends a switch request message to an unassociated neighboring AP. The switch request message includes an identifier of a mobile terminal and a designated channel. The unassociated neighboring AP switches from an original working channel of the unassociated neighboring AP to the designated channel and monitors the mobile terminal according to the identifier of the mobile terminal so as to acquire application information.