Abstract: 4 full-scale specimens were designed in order to study mechanical properties of the semi-rigid composite exterior joint with the end-plate connection at which the plate is inserted between the end-plate and the column flange. In 3 of 4 specimens, the plate thickness is 6mm, 9mm or 12mm respectively. The other specimens has no the plate for comparison. The low-cycle loading experiment controled by the horizontal displacement of the column top is conducted and the effect of the inserted plate on mechanical properties of the semi-rigid composite exterior joint with the end-plate connection is analyzed in this paper. The results show that the effect of the plate can be neglected when the plate thickness is less than the end-plate thickness, and the effect of the plate is obvious when the plate thickness is greater than or near the end-plate thickness. Therefore, the usage of the thick plate should be avoided as far as possible in the actual construction.