The invention discloses a braking device of a fuel pressure control braking valve. The braking device comprises a fuel pump, a high-pressure fuel rail, a pressure sensor, a plunger spring, a plunger and barrel assembly, a low-pressure ring slot, a fuel tank, a swing arm, a tappet and an exhaust valve. The fuel pump communicates with the high-pressure fuel rail, the high-pressure fuel rail communicates with the plunger and barrel assembly through a fuel outflow pipe, the fuel tank communicates with the plunger and barrel assembly through a low-pressure fuel way, the swing arm is located between the plunger and barrel assembly and the tappet, the plunger is located above the same end of the swing arm, and a valve tappet of the exhaust valve is located below the same end of the swing arm. The pressure sensor is arranged at one end of the high-pressure fuel rail, and pressure of fuel in the high-pressure fuel rail is detected in real time. Due to the fact that the pressure of the fuel in the high-pressure fuel rail is high and stable, the timeliness and stability of decompression braking can be improved, meanwhile, the tappet does not need to compress lubricating oil, the tappet does not need to be treated through a special process, and the cost is reduced.