The dynamic computer-generated holographic imaging system with spatial light modulators (SLM) is considered as a special coherent imaging system, and the point spread function (PSF) of this system is derived. Based on the PSF, the apodization and the enlargement caused by the pixelated SLM are analyzed, and the influences of the fill factor of SLM and the diffraction distance on the resolution of this imaging system are investigated by computer simulation. Moreover, the minimum diffraction distance required for sampling theorem is also considered, and a pretreatment method for eliminating this influence is reported. This works is meaningful to the perfection of this system.