In order to investigate the seismic behavior of diagonal-reinforced coupling beams with a small span-depth ratio， the equivalence of the two reinforcement arrangements （individual diagonal reinforcement and full diagonal reinforcement） is verified. Six RC diagonal-reinforced coupling beams were tested under cyclic loading considering the effect of variable parameters such as span-depth ratio and layout of reinforcement. Test device adopts double wall-column loading， so that the coupling beam can realize equal double curvature bending. The test results show that the failure mode changed from bending failure to shear failure with the decrease of span-depth ratio， and ultimate rotation decreased from 4.89% to 1.98%. Two types of diagonal reinforcement coupling beams have close mechanical performance. The limit of shear compression ratio in national code JGJ 3 is reasonable. Based on a database analysis of diagonal-reinforced coupling beams， a new shear capacity formula is obtained. The new calculation formula is more accurate than that in current standard， and reflects the force mechanism better.