Abstract: With the increase of service time, prestressed concrete beams under corrosive environment attacking will gradually exhibit the deterioration of ductility and load bearing capacity due to the corrosion of stressed tendons in erosion environment, which seriously affects the safety of building structures. In order to study the load bearing capacity of prestressed concrete beams under a corrosive environment, the corroded prestressed concrete beams under concentrated loads was taken as the research object, and the deteriorated property of corroded materials and the effect of prestressing for load bearing capacity were analyzed. Based on the truss-arch model, the distribution coefficients of truss role and arch role were calculated, and the calculation formula for load bearing capacity along with the assessment method of failure mode of the prestressed concrete beams were proposed. The experimental data of 76 prestressed concrete beams were used to validate the suggested model. The results show that: for the load bearing capacity of prestressed concrete beams, the calculated values are in a good agreement with the test values, and the mean value and the variance of the ratio between them are 1.116 and 0.033, respectively. Using the proposed model, the prediction of the failure mode agrees well with the observed failure mode of experimental concrete beams, and the suggested method can reflect the fact that the failure mode of the concrete beams changed by time as the corrosion degree increases. Thus, the proposed model can be applied to calculate the load bearing capacity and assess the failure mode of corroded prestressed concrete beams.