A novel force control method was proposed based on the Magnetorheological torque-servo (MRT) to control the polishing force to maintain a polishing pressure constant in precise NC polishing of aspheric parts. The mechanism, model and affect factors of the method were investigated,and a corresponding polishing system was developed. Firstly, the mechanism of the polishing force control method based on the MRT was presented. Then the principle of constant pressure polishing was analyzed by using Preston equation,and the model of polishing pressure was established according to Hertz theory. Finally, the control model of polishing force was deduced to realize the constant pressure polishing, and the affecting factors of model were discussed. Experimental results indicate that the surface roughness of the part improves from initial value 1.6 μm to 0.067 μm and 0.028 μm respectively, and the unevenness of surface roughness is 94.4% and 11.4%, respectively after polishing with the constant force and constant pressure and the polishing time in 90 min, which means the polishing quality and effciency have been improved greatly. It is concluded that the method can control the polishing force and polishing pressure independently, actively and real time and can improve the surface quality of parts remarkably.