Abstract: In order to detect the performance of infrared lens accurately and rapidly, an auto focus measurement system with rapid infrared CCD was put forward, based on image processing. In this system, mid-wave cooled infrared CCD was used, whose wave length ranges from 3.7-4.8 m. The infrared CCD received the radiation which came through the detecting infrared lens, auto focus and image processing. By using the technology of auto-focus and image processing, the performance of the lens such as symmetry or focus and so on would be test. In this article, the modern auto-focus methods were emphasized, and the auto focus method suit for this detection system was put forward. A new image clarity evaluation organically combined grey entropy with statistics function was described, and was verified by a lot of testing results. The experimental results show that the position precision of the system resetting is up to 10 m.