Abstract: According to the complex surface shape of free-form surface optical elements, this paper proposes a method for obtaining the optimum pressure field in magnetorheological polishing. Firstly, the influence factors of the pressure field in the polishing area of the magnetorheologically polished free-form surface optical element are obtained by analyzing the pressure field. Secondly, combined with the influence factors of the pressure field, a quantitative morphological evaluation method of the pressure field is established based on the geometric intersecting theory. Based on the geometric model of the free-form surface, the method is respectively applied to the plane, the spherical surface with different curvatures and the free-form surface. Analysis of different immersion depths and different angles is performed to obtain the corresponding pressure surface shape, and then the pressure field morphological evaluation calculation is carried out. Finally, Analysis of the obtained experimental data proves that the method can well characterize the morphological parameters of the pressure field.