To analyze the moment-rotation relationship of the representative asymmetric mortise-tenon joint to through-tenon joint with gap, an embedment model of joint was constructed. The moment-rotation calculation formula of through-tenon joint was deduced by establishing the relationships of forces, materials and geometries. Existing tests approved that the theoretical calculation results agreed well with the test results. Furthermore, the effects of the gap g and the friction coefficients μ on bending moment and initial rotation stiffness of the joint were analyzed quantitatively, and the results showed that: the positive and negative initial rotation stiffness of the through-tenon joint decreased with the increasing gap g, and there is a linear change between them. The bending moment and rotational stiffness of the joint increased as the friction coefficient increased under the positive and negative loading, and they have a significant change, especially when the joint yields. Gap in joint is a main influence factor on the bending moment and rotational stiffness of the joint, and the influence of friction coefficient on the bending moment and rotational stiffness of the joint is slightly less than that of the gap. The study in this paper provides theoretical basis for the mechanics analysis of ancient timber framed buildings.