Abstract: Channel-casing can effectively improve the capacity and stiffness of joints, which can be used for local reinforcement of steel tubular joint in service. To study the in-plane bending performance of channel-casing reinforced SHS (square hollow section) joint, 5 SHS X-joints with a brace-to-chord diameter ratio β of 0.58, 0.7 and 1.0 were tested under in-plane bending load. The results show that the channel-casing reinforcement can effectively improve the bending performance of joints. When β=0.58 and β=0.7, the bending capacity of channel-casing reinforced joints increases by 37% and 163% respectively. The stiffness of reinforced joints is slightly lower than that of the joint with equal width, but its ductility is better. The brace-to-chord diameter ratio and the thickness of the channel-casing are two key parameters influencing the in-plane bending behavior of the reinforced joints. And the reinforcement of channel-casing can effectively protect the chord of the joint, which leads to the transformation of failure mode of specimens from the failure of chord or welding seam to the failure of brace. Further mechanism analysis shows that the channel-casing can form a common bearing carrier with a chord wall, which improves the bearing capacity and stiffness of the joint owing to local thickening. Finally, the applicability of the formulas for calculating the flexural capacity of the channel-casing reinforced joints are compared and analyzed, and suggestions for design are proposed.