Abstract: Studying the shear mechanism of rock mass is the foundation for predicting the shear strength of rock joints.The contact distribution law of micro convex body in the process of direct shear test of joint surface was inverted by numerical tracking technology.The contact angle, contact area and contact position were analyzed, and the relationship between the average contact angle and joint roughness coefficient(JRC)value was established.In this process, the following conclusions were obtained.(1) From the view of contact angle corresponding to peak shear stress, the influence of normal stress on the contact angle was not significant, and the contact angle was influenced by contact morphology.The shear stress was positively correlated with the average contact angle, and the average contact angle and the maximum shear stress both reached their largest at the same time.(2) During the shear process, most(more than 90%)shear positions occurred on the side of the micro convex facing towards the shear direction, and a little of contact area occurred on the side away from the shear direction.(3) Using the average contact angle to determine the JRC value and then predict the joint surface strength had a high accuracy, and the average error was less than 5%,showing satisfactory accuracy and rationality.