In this paper, a NC compliant abrasive polishing system was developed based on a magnetorheological torque servo (MRT), using a bonnet as the polishing tool. The MRT was uesd to provide a load acting on bonnet tool to produce the polishing force. In order to find the factors affecting the polishing quality, the models of the applied load, polishing force and contact pressure between the bonnet and the part were established based on Hertz theory, and the factors affecting the contact pressure were analyzed. Theoretical analysis indicated that there was a significant effect of the applied load, the initial pressure of the bonnet and the radius of curvature of the part on contact pressure. Experiments were carried out to verify the validity of the models, and experiment results showed that the roughness of the part was improved greatly and the polishing efficiency could be controlled by changing the initial pressure of the bonnet and applied load.