The invention discloses an engine braking improving device, which consists of an exhaust valve control mechanism that is composed of a driving force input wheel, a cam wheel driven wheel, a rocker and a rockshaft, wherein the driving force input wheel is arranged outside the cam wheel driven wheel; the other end of the rocker is provided with a horizontal driving piston, a vertical valve play regulating piston and a vertical braking plunger; a connecting rod of which the two ends have convex spherical surfaces is arranged between the driving piston and the braking plunger; the convex spherical surface of the upper end of the connecting rod is fit with the concave spherical surface of the driving piston; the convex spherical surface of the lower end of the connecting rod is fit with the concave spherical surface of the braking plunger; and a valve rod connecting piece of the exhaust valve is arranged below the braking plunger. The driving force input wheel transfers the engine power tothe rocker periodically, the switching between a braking mode and a normal operation mode can be realized by using the gap between an electromagnetic valve control rocker and the valve rod connectingpiece of the exhaust valve, the volume and weight of a brake are reduced, and high oil pressure and the leakage, deform and load fluctuation which are caused by the high oil pressure are avoided.