Abstract: The failure of infilled rock joints can be divided into interface damage and filling damage, which one dominates depends on the stress conditions of the two parts. When the filling was damaged, its plane stress state was analyzed. A theoretical shear strength formula was obtained and the effects of normal stress and filling thickness were studied. With the increase of normal stress the shear strength of infilled rock joints increases first and then decreases, but the influence of filling thickness is not obvious. Some direct shear tests of infilled rock joints were also carried out. The results show that the shear strength is related to the failure modes of the joints, and under the same mode it is independent of filling thickness.