Spatial light modulator (SLM) is an alternative product as it can change the distribution of amplitude, phase and polarization state under the control of the electric signals. In recent years, SLM is used in aspheric testing in place of the computer generated holography (CGH) plate. However, SLM pixel pitch is around 3.5~20 μm, which is much larger than the CGH plate etching resolution and the phase modulation is discrete, error existing with ideal continuous phase modulation and causing detection accuracy reduction. So it is necessary to consider the influence of SLM pixel pitch on detection accuracy so as to choose SLM with proper pixel pitch. Wave-front reconstructed by SLM and spread to the measured surface process is simulated based on Fresnel diffraction theory and fast Fourier transform algorithm. And the relationship between the reference wave-front precision and SLM pixel pitch is analyzed. Several sets of wave-front are computed and the error distribution is analyzed. The conclusion is that the SLM generation compensation wave-front is related to the maximum frequency presented by SLM pixel pitch, and it is necessary to keep the maximum frequency presented by SLM pixel pitch above the compensation wave-front maximum frequency range.