A dry connection method for horizontal joints of fully assembled composite walls is proposed in this paper. The prefabricated wall and the upper and lower structure are connected by pre-buried steel parts, L-shaped steel plates and high-strength bolts. In order to study the seismic performance of the composite wall and the mechanical behaviour of the joints, 5 specimens were designed with the thickness of steel plate and the high-strength bolt specifications (diameter and pre-tension) as key parameters. A monotonic loading test was performed to study the failure mode, horizontal load-displacement curve, eigenvalue point, seismic performance index, strain of the joint, and relative slip of the joint and the wallboard of the test piece. The results of experimental research show that the specimens with bolted connections on horizontal joints have strong deformation ability, where the ultimate displacement angle is up to 1/25, and they still have high bearing capacity. Increasing the thickness of jointed steel plates can improve the bearing capacity and initial stiffness of the specimens, but the specifications of the high-strength bolt have no obvious influence on the bearing capacity and rigidity of the specimen.