As an essential component of lifeline systems

water supply system plays a more and more important role in modern city.Unfortunately

it suffered extensive damage during many previous earthquakes.Therefore

study on the seismic reliability of water distribution system is an important topic in the earthquake engineering field.The seismic hydraulic analysis of the urban water supply system can serve the economic loss forecast and disaster control after earthquake.In this paper

a hydraulic analysis program of the water supply system in an earthquake is developed based upon the hydraulic analysis method in a normal state.As a significant factor affecting the result of the hydraulic analysis

the pipe leakage area is used to describe the damaged state of a buried pipe in the earthquake.After introducing the experiential leakage model

Chinese model

which was often used in the capability analysis

a new leakage model based on seismic response analysis of buried pipeline is presented in this article.Apply this model into the analysis of the water supply system and combine it with the first order second moment（FORM） reliability method

a new method of analyzing the capability reliability of a water supply system is suggested.In order to validate the proposed method

a network with 17 nodes and 24 pipelines is studied to compare the difference between the new model and the traditional experiential Chinese model.The results show that the Chinese model which comes from the leakage flux under normal state of water supply system will overestimate the capacity reliability under earthquake.On the other hand

the algorithm with the new leakage model presented in this paper can make the seismic hydraulic analysis efficient and accurate.The results proved that the method put forward in this paper is qualified for analyzing the seismic reliability of water supply system.