The invention discloses a double-acting retarder, which comprises a frame, a speed changer and a transmission shaft, and the double-acting retarder is characterized in that an output shaft of a speed changing box is connected with a cam and a brake disc body, two sides of the cam and the brake disc body are respectively and symmetrically provided with a plunger pump, the plunger pumps are connected with a heat radiating oil tank through an oil inlet pipe with a one-way valve A, the oil inlet pipe is connected with a one-way valve B through a tee joint, the other end of the one-way valve B is connected with a brake device through an oil outlet pipe, the oil outlet pipe is also connected with a throttling valve through a tee joint, the throttling valve is connected with the heat radiation oil tank through an oil return pipe, the outer side of each plunger pump is wrapped by a brake slide groove, a thrusting air chamber is arranged between the bottom end of each plunger pump and the brake slide groove, the front end of each plunger pump is provided with a guide wheel, the guide wheel is matched with the came and the brake disc body, the thrusting air chamber is connected with an air storage tank through a retarding switch, and both the retarding switch and the throttling valve are connected with a control unit.