To explore the influence of milling-grinding processes on the surface damage layer of infrared silicon lenses and enhance the surface machining quality, a spatial motion trajectory model of abrasive grains in grinding tools is constructed. The removal mechanism of the surface damage layer during lens milling-grinding is systematically analyzed, and the key factors such as grinding wheel speed, workpiece rotation speed, axial feed rate of the grinding wheel and milling depth affecting surface machining quality are identified. Horizontal process experiments are designed, and orthogonal experimental methods are employed to validate the theoretical analysis. Results show that the degree of workpiece surface damage is positively correlated with machining radius, axial feed rate of the grinding wheel, and milling depth, while negatively correlated with workpiece rotation speed and grinding wheel speed. Optimizing process parameters can effectively reduce surface roughness, minimize surface shape errors, and improve the surface machining quality of infrared silicon lenses.