The invention discloses a quick-braking engine brake device, which consists of an exhaust valve control mechanism, wherein the exhaust valve control mechanism consists of a driving force input cam, a cam driven wheel, a push rod, a rocker arm and a rocker arm shaft; one end of the push rod is connected with one end of the rocker arm; the cam driven wheel is arranged on the other end of the push rod; the driving force input cam is arranged outside the cam driven wheel; the other end of the rocker arm is provided with a horizontal driving piston and a vertical braking piston cylinder; a circular groove is formed on the middle part of the driving piston; a lateral side of the circular groove and the lateral surface, on the left of the circular groove, of the driving piston serve as a non-working face and a working face to contact the upper end face of the braking piston cylinder in a pressed way respectively; and a valve rod connector of an air exhaust valve is arranged below the brakingpiston cylinder. The driving force input cam transmits the power of an engine to the rocker arm periodically, the gap between the rocker arm and the valve rod connector of the air exhaust valve is controlled by an electromagnetic valve to realize switching between braking and normal working two states, so that the volume and weight of the brake are reduced, and high oil pressure and leakage, deformation and load fluctuation caused by the high oil pressure are avoided.