In order to explore the enhancement effect of new materials on the performance of steel structures, the flexural behavior of steel beams under load is analyzed by strengthening and transforming the steel beams with Reinforced Reactive Powder Concrete (RPC). Through the bending test of the test beam under the secondary load, the failure process of the beam was analyzed. Then, the influences of initial load, RPC strength, and section steel strength on the bearing capacity of beam were studied. The test results were verified by the finite element simulation. The research shows that under the influence of different parameters, the bending capacity of the steel beam wrapped by reinforced RPC is 1.7~2 times higher than that of the pure steel beam and the specimen shows better ductility during the failure process. Meanwhile, no bond failure occurs at the interface between the section steel and the RPC, and both can work well together. The ultimate bearing capacity of the beam decreases with the increase of the initial load and increases with the increase of RPC strength and section steel strength. According to the experimental results, the calculation formula for the flexural bearing capacity of steel beam wrapped by reinforced RPC under the secondary load and the RPC strength reduction formula are proposed. The experimental value, the calculated value and the simulated value are in good agreement.