Abstract: Considering the complexity of urban infrastructure system, the pair-comparison matrix was introduced with multi-attribute decision making theory based on standardizing data to evaluate the risk of urban infrastructure accident. The aim of this article was to find the key risk factors in urban infrastructure accident, and provide decision support for managers. The urban water-supply system was also taken for example to solve this question with the analytic hierarchy process. The result shows that the biggest risk of water-supply comes from water supply network, and the second important factor lies in water conveyance system. Among the risk factors of water supply network, water pollution is the key factor, and the short of water supply is the factor which has the least potential risk.