laser forms a smaller diameter spot in the diffuse reflection screen. By using the light meter to measure the spot illumination, artificial multiple operations is likely to cause errors. This article uses digital photography, calculating the image intensity of the spot camera, establishing the spot illumination and gray of the mathematical mapping model and deriving the mathematical formula based on the Tsai model. The method is simple and accurate. Through experiments and data analysis, the experimental results show that illumination mapping of the location of points and the image corresponding to the gray spot on the CCD response linear relationship provide a new reference for the mapping of the diffuse reflection screen illumination and CCD image gray value.