The invention discloses an air conditioner, a return air plate assembly thereof and a control method of the return air plate assembly. The return air plate assembly comprises a fixed plate, a lifting plate, a lifting mechanisms, a locating mechanism, a receiving unit and a control unit, wherein the lifting plate is provided with a return air grille; the lifting mechanisms is are connected between the fixed plate and the lifting plate; the locating mechanism comprises a first locating piece arranged on the fixed plate and a second locating piece arranged on the lifting plate; the receiving unit is used for receiving an instruction of a user; and the control unit is used for controlling the lifting mechanisms according to the instruction of the user to enable the lifting plate to lift between a using position matched with the fixed plate and a falling position located below the fixed plate and is also used for controlling the second locating piece and the first locating piece to be matched for location when the lifting plate lifts to the using position so as to limit the lifting motion of the lifting plate. Therefore, through controlling the lifting mechanisms and the locating mechanism by the control unit, the lifting plate can be conveniently cleaned by a worker, the operation safety can be improved, and meanwhile the problem that the lifting plate possibly falls off can be solved, so that the working reliability and using safety of the lifting plate are effectively improved.