Abstract: RQD is an important index for evaluating the integrity of rock masses. The traditional methods are greatly affected by drilling process, core quality and run length, and cannot objectively reflect the quality of rock masses. To solve this problem, An automatic RQD analysis method based on the edge threshold segmentation of borehole images is proposed. This method first performs preprocessing and edge threshold segmentation on the borehole images to achieve target screening. Then, encode the screened target area is encoded, and the connected areas are merged to determine the effective targets that affect the RQD analysis. Finally, the location and width of the structural plane and fracture zone are extracted, and the RQD of boreholes is calculated. For a case study of the Dongzhuang Dam at Jinghe River, the automatic RQD analysis is performed, and the achieved results are in good agreement with the borehole images and the coefficient of rock mass integrity. The proposed method improves the accuracy of RQD statistics, enriches the acquisition of RQD, and provides a fast and effective method for evaluating the rock mass integrity.