The invention provides a torque control method, device and system for a light mixing system, and relates to the technical field of engine mixing. The method is applied to a three-cylinder engine witha BSG motor, and comprises the steps of calculating torque increasing torque and the maximum available torque of the BSG motor under the current situation when a torque increasing request is received,wherein the torque increasing torque is a difference between a current output torque and a target torque corresponding to the torque increasing request; judging whether the maximum available torque is larger than or equal to the torque increasing torque or not; if yes, controlling the BSG motor to output the torque according to the torque increasing torque; if not, controlling the BSG motor to output the torque according to the maximum available torque and controlling the three-cylinder engine to output the torque according to the difference between the maximum available torque and the targettorque. According to the torque control method, device and system for the light mixing system, the BSG motor is preferentially selected for torque increasing, when the torque of the BSG motor cannotmeet the request completely, the requested torque is met by controlling the engine, and the fuel economy can be improved.