Digital Moiré patterns filter processing is a key technique of aspheric testing by using the Moiré patterns, and the filtering result immediately influences the precision of aspheric testing. The discussion analysis is carried on from the spatial domain and the frequency domain. And the modeling is also carried on. The root mean square (RMS) of the full aperture phase distribution residual error is seperately 0.024λ and 0.035λ, and the results show that the filtering method is feasible.