Abstract: The difficulties of digitally evaluating surface defects of optics using American military standards MIL-PRF-13830B lie in judgment of surface defects concentration. For this problem, we raised a kind of judgment algorithm of surface defects concentration. The algorithm uses the method of overlap of weight region. It seeks circular area where defects are dense by means of attaching weight region for surface defects, and turns overlap of weight region into position judgment and calculation between matrixes, which makes full use of convenience of matrix operations. In experiment, using this algorithm judged quartz standard board where information of defects was known, and the circular area where defects were dense was accordant with expectation, which validated the correctness of the algorithm. At present, the algorithm have been used for precise surface defects digital evaluation using American military standards in optical workshop.