Hoop head tenon-mortise joint is extensively adopted in an ancient timber structure in Guangfu, which is different from straight tenon-mortise joint or dovetail tenon-mortise joint in terms of mechanical performance. To analyze the mechanical properties of hoop head tenon-mortise joint，mechanism analysis was carried out and the moment-rotation calculation formulae were also derived, while the formulae were verified by experimental results. Using the formulae，the factors affecting the relationship of moment-rotation of hoop head tenon-mortise joint were investigated. The results indicate that within the range of parameters, the initial rotational stiffness and ultimate bending moment increase with the increase of the column diameter, mortise width, friction coefficient and unilateral compression width between tenon and mortise，while the ultimate bending moment increases with the increase of beam height, but the initial rotational stiffness is only slightly affected by the beam height. The results of this study can serve as a theoretical foundation for mechanical analysis as well as for seismic research of ancient timber structures in Guangfu.