| The flexural tests of three ultra-high performance concrete-normal concrete (UHPC-NC) composite beams that ultra-high performance concrete (UHPC) was located in the tensile zone and one ordinary reinforced concrete beam were carried out. The stress process, the strain distribution in the mid-section, the crack development mode and the failure mode of the UHPC-NC composite beam were studied and analyzed. The test results show that the UHPC-NC composite beam basically conforms to the sectional assumption during the loading process, and the proper amount of longitudinal steel bars in the UHPC layer can greatly improve the flexural resistance of the composite beam. At the same time, the contribution of reinforcement and UHPC to the ultimate bearing capacity of test beam was calculated in four stages (initial state, stage state, ultimate state and failure state). Finally, the equivalent rectangular stress coefficient k of the UHPC layer in the tensile zone of the composite beam was derived. The results show that the contribution efficiency of the UHPC layer to the flexural resistance of the composite beam varies with the ratio of reinforcement.