In order to study the effects of wedge on the seismic performance of loosen joints, three full-scale penetrated mortise-tenon joint models are made, including a standard joint, a loosen joint and a loosen joint with wedge respectively. The deformation and failure characteristicses of three joints are compared. Hysteresis curves, skeleton curve, stiffness degradation law, energy dissipation and ductility of three joints were analyzed by full scale quasi static test as well. Results show that mortise can pull out of tenon partly during rotation, and transverse compression deformation occurs to tenon at the contact part between mortise and tenon. Failure mode is wood fiber torn along the grain at variable cross-section. Loosen joint have obvious slipping phenomenon, which decreases after adding the wedge; Hysteresis curves of loosen joint has obvious pinch effect, which decreases after adding the wedge; External load resistance capacity and energy dissipation capacity of loosen joint are obviously lower than that of standard joint, and the above performances of joint have an rising trend after adding the wedge. While the above performances still slightly lower than that of standard joint. The results can make a solid foundation for the state assessment and seismic strengthen of traditional timber structures.