The algorithm of partially overlapped sub-block histogram equalization is an effective algorithm for image enhancement.Firstly,the infrared image is divided into many small sub-images,and then each of these small sub-images is enhanced by histogram equalization.These processes will result in mosaic effect,and the mosaic will be solved with special processing.Because every small sub-image is processed separately,it will take a long time to finish the work.This paper researches the optimizing algorithm of partially overlapped sub-block histogram equalization.It reduces the processing time to a large scale and improves the working efficiency.