Due to pollution in second water supply system (SWSS), nine renovation alternative plans were proposed and comprehensive evaluations of different plan based on Analytical Hierarchy Process (AHP) were presented in this paper. Comparisons of advantages and disadvantages among the plans of SWSS renovations provided solid foundation for selecting the most appropriate plan for engineering projects. In addition, a mathematical model of the optimal combination of renovation plans has been set up and software Lingo was used to solve the model. As a case study, the paper analyzed 15 buildings in Tianjin City. After simulation of the SWSS renovation system, an optimal scheme was obtained, the result of which indicates that 10 out of those 15 buildings need be renovated in priority. The renovation plans selected for each building are the ones ranked higher in the comprehensive analysis. The analysis revealed that the optimal scheme, compared with two other randomly calculated ones, increased the percentage of service population by 19.6% and 13.6% respectively, which significantly improved social and economical benefits.