Abstract – With great economic value and practical value, the road crack detection is critical for road rehabilitation. In this paper, an improved Otsu threshold crack detection method based on gray histogram is proposed. By modifying the probability weighting factor of the gray histogram, the proposed method improves the accuracy of target extraction, avoids the problem of prominent peaks, solves the problem of road image processing of various crack types. The experiment results show that the proposed method not only has good consistency in detecting cracks on different pavements, but also has fast calculation speed.