Abstract: To investigate the seismic behavior of reinforced concrete (RC) beams with high ductility concrete (HDC), eight RC beams were designed and strengthened with HDC jackets and carbon fiber strips. The failure modes, deformation capacity and energy dissipation capacity of the specimens were studied under low cyclic loading tests. The experimental results show that: The tensile strain hardening and multiple cracking of HDC can effectively control the development of shear cracks of the beams strengthened with HDC during the failure process and the HDC-strengthening system is effective to improve the brittle failure characteristics; HDC can provide obvious constraint for the core concrete. The shear strength, ductility and energy dissipation capacity of the strengthened beams are significantly improved. The HDC jacket could be more effective than the carbon fiber strips in enhancing the behavior of the beams; When the shear span is relatively large, using mesh reinforcements in the HDC jacket improves the ductility and energy dissipation capacity. However, it contributes little to the shear capacity. A calculation method for the shear capacity of strengthened beams is proposed based on a truss-arch model. The calculated results have good agreement with the test results.