The calculation of the photometric characteristics such as image plane′s illumination and contrast are presented according to the demand of photoelectric imaging deflection measurement system. The relationship between the source, background radiation, optical system and image sensor is analyzed. Illumination and contrast on the image plane of camera are also discussed when replacing the system′s source with high reflectivital material or using material with low reflectivity replacing background. The result contributes to putting forward the method of photometric design of photoelectric imaging deflection measurement system.