The invention discloses a vehicle hybrid power system and a control method thereof. The system involves an engine, a hybrid power module and a double-input-shaft speed change mechanism, wherein the hybrid power module is composed of a motor, a planetary gear train and a first clutch, the planetary gear train is provided with at least three rotating shafts, the three rotating shafts comprise a rotating shaft X1, a rotating shaft X2 and a rotating shaft X3, axes of the three rotating shafts are on one straight line, the rotating speed of the rotating shaft X2 is between the rotating speed of therotating shaft X1 and the rotating speed of the rotating shaft X3, a first clutch is arranged between any two of the three rotating shafts, a power output shaft of the engine is connected with the rotating shaft X3 or the rotating shaft X1 of the planetary gear train and a second input shaft of the double-input-shaft speed change mechanism, a rotor of the motor is connected with the rotating shaft X1 or the rotating shaft X3, and the rotating shaft X2 is connected with a first input shaft of a double-input-shaft gearbox. According to the system and the method, the transmission efficiency is high, multiple gears are provided, the three-axis double-freedom-degree planetary gear train is introduced, a vehicle is driven to start by the differential between the engine and the motor, starting of the vehicle is stable, the smoothness of gear shifting is good, and the impact of gear shifting is small.