Abstract: In order to provide technical foundation for using widely synthetic macro-fiber in earthquake region, this paper studies on the seismic performance of synthetic macro-fiber reinforced concrete beam under low reversed cyclic loads by the experimental method, and emphasizes on discussing the failure pattern, characteristic loads and deflections, ductile, stiffness degradation and energy dissipation capacity, ductile evaluating method of synthetic macro-fiber reinforced concrete beam is analyzed. the ductile index of synthetic macrofiber reinforced concrete beam is larger 49% than that of plain concrete beam, and presents good seismic performance.