It is closed hydraulic system made up of axial hydraulic pump and motor. The pump is variable pump with charge pump and the motor is fixed-displacement or variable-displacement motor with valve assy.  The control way of changing displacement includes MDC, HDC and EDC which can efficiently control the discharge, direction and power of the output oil. The hydraulic transmission system made up of this series of pump and motor has features of wide work range, reliable working state, easy operation and can be widely used on the hydraulic apparatus of engineering machine, agricultural machine, mine machine, aviation and transport machine