On the basis of indentation fracture mechanics, a theoretical model was developed to evaluate the relationship between surface roughnesses (SRs) and Subsurface Damage Depths (SSDs) of brittle optical materials and to predict their grinding induced SSDs. For validating the feasibility of this method, the SSDs generated with various process parameters were measured by Magnetorheological Finishing (MRF) wedge technique. The influences of processing parameters on the SRs and SSDs were investigated, and a process strategy was also proposed to improve the material removal rate. The prediction results of this theoretical model show that the SSDs are nonlinear monotone increasing with the square of SR values during grinding processes. The SSDs and SRs increase with the increasing of cutting depth and feed rate, while reduce with the increasing of spindle speed. The measurement results of SSDs are consistent with the prediction values of the model, which demonstrates the feasibility of utilizing this model to accurately and non-destructively predict the SSDs.