Abstract: Compared with traditional machining machine tools, the stiffness and the positioning accuracy of robot were low. In order to improve the machining quality of robot assisted grinding, it was necessary to control the contact pressure in the machining process. Taking the depressing amount of the grinding tool as the independent variable, the contact pressure between grinding tool and workpiece as the dependent variable, the finite element simulation was carried out based on the contact characteristics of spherical elastic grinding tool during grinding. The curve fitting of the downforce contact pressure simulation results was carried out, and its accuracy was verified by the contact experiment. The impedance control model modified based on the environmental model was established, and the free-form surface force control experiment was carry out. The results show that the impedance control method based on environmental model modification can effectively improves the force control performance of the spherical elastic abrasive tools, and the free-form surface force control accuracy reaches ±0.5 N, which provides stable grinding pressure for the complex surface grinding of the spherical elastic abrasive tools.