The utility model discloses a two separation and reunion series -parallel connection hybrid power system of unipolar, including engine, driving motor, generator, derailleur and group battery, the group battery provides electric power for driving motor, and the generator is used for charging to the group battery, driving motor's rotor passes through driving motor axle head clutch as power shaft one end engine drive shaft, the power shaft other end connect the input shaft of derailleur, the axis of rotation of generator is passed through the clutch and is connected a control circuit connection with engine drive shaft the clutch of driving motor axle head clutch and generator, the utility model provides a more compact solution has been solved ISG and has been mixed in the movable mould type function and the partial defect of performance, has solved simultaneously that the ISG technique can not realize or has hard realized the not enough defect of continuation of the journey mileage under the ECO mode. Be applicable to city low -speed, wriggle go, frequent start -stop operating mode, can exert the engine maximum efficiency simultaneously, reduce and discharge and the oil consumption, extension engine life.