In order to study the effects of wedge on the seismic performance of loose joints, three full-scale penetrated mortise-tenon joint models are made, including a standard joint, a loose joint and a loose joint with wedge respectively. The deformation characteristics and failure characteristics of three joints were compared and analyzed through laboratory full-scale tests. 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 the failure mode of standard and loose joint is wood fiber torn along the grain at variable cross-section.The failure mode of the joint with wedge is the extrusion failure of wedge.The slipping phenomenon and pinch effect of hysteresis curve decrease after adding the wedge. External load resistance capacity and energy dissipation capacity of loose joint are obviously lower than that of standard joint, and the above performances of joint have a rising trend after adding the wedge. The bending moment of the joint with wedge is about 30% higher than that of the loose joint.