Abstract: With the aim of developing one new and efficient structural strengthening method for reinforced concrete (RC) , this study applied a new high performance composite material, high-strength strand mesh reinforced engineered cementitious composites (HSSM-ECC), to strengthen RC beams; conducted the flexural performance experiment of damaged RC beams strengthened with HSSM-ECC; and analyzed and calculated the cracks of the strengthened beams based on test results. Experimental parameters include the damage degree of the original RC beam, the diameter, and the reinforcement ratio of the steel strand. The test results show that strengthening the damaged RC beam with HSSM-ECC can better restrain the crack development of the original beam, reduce the crack width, and significantly improve the bearing capacity, the stiffness and deformation capacity of the original beam. By the way of reducing the damage degree of the original RC beam, of increasing the reinforcement ratio of longitudinal steel strands within a reasonable range, or of using steel strands with smaller diameter can improve the restraining ability of the reinforcement layer to the cracks of the RC beam. Combined with relevant mechanics theory, the calculation theory and one formula for maximum crack width of damaged RC beams strengthened with HSSM-ECC in unloading conditions are proposed, which are in a good agreement with experimental results.