Abstract: Under the attack of various aggressive environmental factors, the durability of material degrades, which leads to the reduction of concrete strength, steel bar corrosion and other durability diseases, resulting in the gradual decline of the safety and reliability of urban bridges. A typical city viaduct was taken as an example, based on the durability theory of concrete structures and the load limit policy of city, combined with the results of in-situ inspection and traffic survey, the time-varying load bearing capacity and load effect of the bridge structure were analyzed, and the failure probability was calculated by referring to the reliability function of the bridge’s control sections, and then the reliability was evaluated. The research method provides reference for the reliability assessment & maintenance of urban bridges and the formulation of traffic load limit policy.