The invention discloses a single valve compressing and releasing type valve bridge braking device. A braking piston is arranged in a braking piston hole in a valve bridge inner end. The lower portion of the braking piston is connected with an inner exhaust door. In the braking process, engine oil enters the braking piston hole, the valve bridge inner end above the braking piston upwards abuts against a rocker arm under the oil pressure, and hydraulic connection is formed between the braking piston and a valve bridge. A braking boss opens the inner exhaust door through the rocker arm, the valve bridge inner end, hydraulic connection and the braking piston, and single valve compressing and releasing type engine braking is generated. The top of an integrated exhaust boss higher than the braking boss further drives the rocker arm, the rocker arm acts on the center of the valve bridge and drives the whole valve bridge to move downwards, the valve bridge inner end is separated from the rocker arm located on the valve bridge inner end, an oil discharging hole in the valve bridge inner end is opened for oil discharging, hydraulic connection between the braking piston and the valve bridge is eliminated, and the valve bridge drives the inner exhaust door and an outer exhaust door at the same time. According to the single valve compressing and releasing type valve bridge braking device, the inner exhaust door is opened for braking, the braking valve lift is reset, the braking load is reduced, and the braking power is increased.