The invention discloses an engine braking method. A cam roller is moved by an axial driving mechanism of the cam roller from a first axial position to a second axial position on a roller shaft, connection between the cam roller and a conventional ignition cam is switched into connection between the cam roller and an engine braking cam, movement of a conventional ignition valve stops, and movement of a braking valve of an engine is generated. The axial driving mechanism of the cam roller can be integrated in a valve actuator such as a rocker arm and can also be located outside the valve actuator; for example, the axial driving mechanism of the cam roller is fixed to the engine. By means of the engine braking method, high-power braking generated by the special braking cam is obtained, the special braking cam can only comprise a braking exhaust cam body and can also comprise the braking exhaust cam body and a braking admission cam body at the same time, engine braking is constructed as non-hydraulic fixed-chain type bearing, and the efficacy losing mode of hydraulic bearing is avoided. The braking control is simple, the braking performance is excellent, the structure is simple and compact, manufacturing and assembling are easy, and the application range is wide.