In order to solve the problem of low processing efficiency due to the over-reliance on manual experience in traditional planar mono-pendulum polishing，the material removal function of workpiece feature points at different relative positions of workpiece and grinding disc is established based on the Preston's principle，and the influence law of workpiece velocity field distribution on planar surface shape is studied. The surface shape of the workpiece is rasterised. The velocity field distribution of the workpiece and the velocity field distribution of the grinding disc are modelled，and the relationship between the velocity field changes at the workpiece's characteristic points and the amount of material removed is simulated using matlab when the workpiece oscillates relative to the grinding disc. A single-factor experimental validation method was used，with a fixed workpiece pendulum amplitude of 0.35 rad，a pendulum speed of 0.09 rad/s and a range of pendulum angles of［0.49 rad，2.79 rad］，for simulation validation. The results show that the greater the difference in the velocity field of the oscillation path of each feature point of the workpiece，the higher the surface accuracy of the workpiece，which provides a new idea and method to find the optimal processing parameters quickly and improve the efficiency of plane processing effectively.