Abstract: Till now, no closed-form theoretical equation of flexural capacity of ultra-high performance concrete (UHPC) beams reinforced with fiber reinforced polymer (FRP) rebars has been proposed worldwide. Based on the concrete damage plasticity model in ABAQUS, a nonlinear finite element analysis model was developed to simulate the flexural performance of UHPC beams reinforced with FRP rebars. The model was verified with available test results. A parametric analysis of 40 UHPC beams was performed and the influence of parameters including cross section dimension, strength of UHPC, tensile strength of FRP rebars and reinforcement ratio on flexural performance were studied. Based on the most widely used standard worldwide French NF P 18-710, the constitutive model of UHPC was simplified and the parameters for equivalent rectangular stress block in compression zone and tension zone were deducted, then the calculation method of balanced reinforcement ratio and the theoretical equations for flexural capacity under compression failure and tension failure were developed for UHPC beams reinforced with FRP rebars. The calculated results from the theoretical equations are in a good agreement with results from tests, finite element analysis and strip method.