In order to improve the flexural behavior and ductility of fiber reinforced polymer (FRP) bars reinforced concrete superposed beams, the effects of steel fiber content and thickness of steel fiber reinforced concrete superposed layer on the FRP bars reinforced concrete beams were studied. The volume content of steel fiber (0%, 0.5%, 1.0%, 1.5%) and thickness of steel fiber reinforced concrete superposed layer (0 mm, 180 mm, 210 mm, 300 mm) were taken as variables. The failure process, failure mode, crack width and mid-span deflection of six FRP bars reinforced concrete superposed beams were analyzed by three-point loading test. The results show that the addition of steel fiber improves the mechanical properties of tested beams and makes failure mode of tested beams develop from brittle failure to ductile failure. With the increase of the ratio of steel fiber and thickness of steel fiber reinforced concrete superposed layer, the ultimate bearing capacity, flexural resistance and ductility evaluation index of FRP bars reinforced concrete superposed beams increase by 9%~33%, 4%~18% and 22%~89%, respectively. Based on the experimental and theoretical analysis, the deflection calculation formula and ductility evaluation method of the FRP bars reinforced concrete superposed beams on the factor of steel fiber are established.