To study the change of flexural capacity of ordinary reinforced concrete beams reinforced with ultra-high performance concrete (UHPC) in different compressive zones, three test beams (reinforced concrete beam RC without reinforced, UHPC reinforced beam UC in compressive zone and UHPC reinforced beam UT in tensile zone) are designed and fabricated, and four-point loading method is used for flexural tests to analyze the failure mode, load-deflection curve and bearing capacity change of the test beam before and after reinforcement. The result shows that compared with the unreinforced RC beams, the stiffness and bearing capacity of test beams UC and UT are greatly improved, in which the bearing capacities increase by 61.2% and 96.9% respectively. A simplified formula for calculating the flexural capacity of concrete beams reinforced with UHPC in compressive zone and tensile zone (considering fiber contribution) is proposed. The error between the calculated value and the test value is less than 5%, which has the high calculation accuracy and applicability.