Deep aspheric optical element can obviously improve the aerodynamic performance of the optical system, thus enhancing and optimizing the comprehensive performance of optical system. The grinding method can be used for primary machining of such elements. However, subsurface damage will be inevitably introduced by this method, and grinding parameters will be changing in real time in the processing of deep aspheric surface, so the depths of subsurface damage of the workpiece are inconsistent. In view of this situation, subsurface damage prediction model was established. Combined with the characteristics of semi-sphere wheels grinding, a theoretical calculation was made to predict distributive regularity of the aspheric grinding subsurface damage depths aspheric characteristics. On the basis of the above work, a simulation experiment on hot-pressing polycrystalline magnesium fluoride plane was carried out. Subsurface damage depths under different conditions of grinding parameters were acquired by the method of magnetorheological finishing spot. Results show that the depth range is between 12.79μm and 20.96μm, which increases from inside to outside along the radius of the workpiece and the results are coincide with previous forecast model.