The remaining service life of reinforced stone arch bridges is of great concern to management and conservation units. It is also the scientific basis for decision to next reinforced maintenance or rebuild. The concept of time-dependent reliability is introduced. Accoding to the most common section enlargement reinforcement method, the load and resistance of the structures are analyzed. The analysis methods and steps of life prediction are proposed, and the remaining service life is obtained. Based on above methods, an engineering example is given, the service life forecast calculation of reinforced stone arch bridges is discussed.