Many kinds of typical crystal defects can be observed in the Cadmium Zinc Telluride (CdZnTe) single crystals. X-ray diffraction topography is a powerful method for the investigation of structural integrity and homogeneity of single crystals. In this paper,reflection X-ray diffraction topography is applied to evaluate the quality of CdZnTe single crystals. The effect of the factors of incident beam slit,exposure time,scanning step and surface roughness on the X-ray diffraction topography are studied. Results show that the incident beam slit is the most important factor to the X-ray diffraction topography of defects,which is also closely related to the application of screening substrates by crystal quality. The parameters of exposure time and scanning step are closely related to the incident beam slit.