A control method of a transmission of an electric vehicle provided with a transmission having a sleeve gear having an inclined chamfer on a first side of the sleeve gear and a flat chamfer on a second side of the sleeve gear, may include measuring a maximum movable stroke of a sleeve having the sleeve gear by moving the sleeve axially to both sides by a controller; determining a reference range to which the measured maximum stroke pertains from predetermined reference ranges by the controller; and determining and setting a neutral position of the sleeve using a predetermined determination method, depending on the determined reference range by the controller.