The invention discloses a power system of a series-parallel hybrid power vehicle as well as a control method and a control system thereof. In the power system, a driving disc of a clutch is connected with an output shaft of an engine; a double-rotor motor comprises an inner motor formed by an inner rotor and an outer rotor as well as an outer motor formed by an outer rotor and a stator, an output shaft of the inner motor is connected with the driving disc of the clutch, and an output shaft of the outer motor is respectively connected with a driven disc of the clutch and a drive shaft of the hybrid power vehicle; a motor controller is electrically connected with the inner motor and the outer motor respectively; and an energy storage system is electrically connected with the direct current end of the motor controller. By applying the double-rotor motor, the installation space and weight of the power system are reduced, and energy saving of the vehicle is facilitated; and by applying the control method and system of the power system, the vehicle can run more smoothly and efficiently, the clutch is not impacted in a clutch combination process, the rotating speed of the engine is kept in an efficient operating range all the time in an acceleration process, the overall efficiency of the system is high, and the design idea of the hybrid power vehicle is met.