The power unit drives the plunger pump in WHPV to realize the conversion from mechanical energy to hydraulic energy; the hydraulic energy is converted from hydraulic energy to mechanical energy through the plunger motor to provide torque for the executing element. The plunger pump and plunger motor form a closed cycle, and the leaking oil is supplied by the filling pump. The output shaft of the plunger motor drives the walking device to realize the functions of forward, stopping and backward of the machine.