The difference of the immersion depth of the planar optical element, the immersion depth of the convex spherical optical element, and the radius of curvature of the convex spherical optical element will change the shear force field at the entrance area of magnetorheological polishing. In order to study the formation mechanism of the shear force field in the entrance area of magnetorheological polishing, firstly establish the necessary fluid model in the magnetorheological polishing process and analyze the geometric characteristics of the entrance area; Secondly, by numerically calculating the different immersion depth and convexity of the planar optical element The influence of different immersion depths of spherical optical elements and different radii of curvature of convex spherical optical elements can obtain the corresponding shear force distribution. Finally, it is concluded that when the certain immersion depth of the planar optical element gradually increases, the shear force at the entrance of the polishing area gradually increases; when the certain immersion depth of the convex spherical optical element gradually increases, the shear force at the entrance of the polishing area gradually increases. Increase; the radius of curvature of the convex spherical optical element has no significant effect on the shear force, and the shear force distribution under different radii of curvature is roughly the same.