The invention discloses a hybrid power system used for a hybrid power automobile. In a pure-electric or hybrid mode, a transmission ratio between a main motor and a power output shaft is variable, therequirement on the rotate speed amplitude of the main motor is low, and only one motor is required. The transmission ratio is changed without changing gear. A shell is internally provided with a dynamic mixer, a control system, an internal combustion engine for driving a hybrid power vehicle to drive and a motor, the dynamic mixer is internally provided with a planetary gear group, and the planetary gear group is connected with the internal combustion engine and the motor through two sun gear shafts respectively; power of the internal combustion engine and the motor is output by the motor ina hybrid mode or independently through the planetary gear group. When the hybrid power system can enable the pure motor to output, the transmission ratio of 2 to 1 or 1 to 1 can be switched; hybrid power output can be carried out at different speeds on the internal combustion engine and the motor, and the output rotating speed is average rotating speed of the rotating speed of the internal combustion engine and the rotating speed of the motor.