The invention discloses a double-assistance circular spherical steering system and a control method thereof. The system comprises a steering wheel, a steering tubular column, a torque sensor, a segment gear, a bidirectional gear and worm reducing mechanism, a steering rocker arm, a steering transverse pull rod, wheels, a vehicle speed sensor, a yaw velocity sensor, an electronic control unit and a left-right assistance motor. In a running process, the electronic control unit acquires signals of the torque sensor, the yaw velocity and the vehicle speed, difference between the perfect yaw velocity and the actual yaw velocity is calculated, the compensation torque of the double-assistance motor is recalculated by a designed adaptive fault-tolerant controller, and a ECU transmits pulse to control running of the adaptive fault-tolerant controller to finish control on stability of an automobile under the normal condition and under the condition that an actuator fails partially. Adaptive fault-tolerant control on the double-assistance circular spherical steering system can be realized, and reliability of the steering system and stability and safety of the automobile during running are improved.