Abstract: In order to predict cumulative damage and residual life of highway bridges under fatigue loads, a simplified numerical simulation method for the deterioration process of in-service reinforced concrete (RC) bridges is proposed. Firstly, based on the rules of degradation of stiffness, strength and residual deformation of concrete and steel during fatigue loading, the envelope equation of the residual strength of concrete and steel in any cycle of a fatigue loading is established. Secondly, according to the uniaxial constitutive model of concrete and the ideal elastic-plastic model of reinforced rebar, fatigue constitutive model of concrete and reinforced rebar are built. At last, on this basis of the improved analytical method of the whole process of a fatigue loading, the numerical simulation method of the failure process of RC bridges under a fatigue load is proposed. A RC beam given as an instance is simulated by using this method and the finite element software of ABAQUS. The results show that the relative errors of both the simulation and experiment are controlled within the scope of engineering errors, which verifies the reliability and availability of the numerical analytical method.