The invention relates to the technical field of vehicles and particularly relates to a braking energy conversion device for a motor vehicle. The braking energy conversion device for the motor vehicle comprises a hydraulic system and an external connection device, wherein the external connection device comprises a wheel device, a hydraulic pump and a clutch, and the wheel device is connected with the hydraulic pump through the clutch; and the hydraulic system comprises an oil way connected with the hydraulic pump, a valve mechanism is arranged on the oil way, and two end parts of the oil way are respectively connected with a fuel tank and an energy accumulator. Compared with the traditional vehicle braking system, the device provided by the invention has the advantage of being capable of converting energy consumed by braking to power for restarting the vehicle, thereby greatly reducing the energy consumption of the vehicle in working. The device can be matched with a traditional braking system and can be reasonably used. In a braking process, the kinetic energy generated by moving of the vehicle can be converted into the hydraulic energy by virtue of the device and can be stored; and in an accelerating process, the stored energy can be utilized by the device to accelerate the vehicle, thereby replacing the energy consumed in the traditional vehicle accelerating process.