In order to investigate the degradation law of the durability of damaged concrete beams, by introducing the fatigue damage factor and the creep damage factor, the calculation model of the corrosion depth of the steel bar after corrosion cracking of the protective layer of the concrete beam with fatigue and creep damage was established. According to the durability design standard of concrete structure, the durability limit state equation controlled by the rust crack width was established. The Monte-Carlo numerical simulation method was used to calculate the reliability of six concrete test beams within the crack width limit. The sensitivity of the four parameters,including corrosion current density, concrete compressive strength, protective layer thickness and steel bar diameter, was calculated using the checkpoint method. The research results show that the reliability decreases from 0.9 to 0.1 with the increase of corrosion time and the increase of holding time for three months has little effect on the reliability of the beam after cyclic loading of 60% of the fatigue life times. The increase of the protective layer thickness and the decrease of the diameter of the steel bar can both improve the reliability of the beam and slow down the decline rate of the structural reliability at the early stage of corrosion of the steel bar. The steel bar diameter of 8 mm can be used as a reference value for the durability design of damaged concrete beams. The sensitivity of the three parameters of corrosion current density, protective layer thickness and steel bar diameter is so relatively large that three parameters are the main influencing factors of durability limit state reliability.