This paper is aimed at a probe into the influential factors and the formulating process of such vulnerability of the urban infrastructure system,so as to disclose ways to reduce such vulnerability and failure rate of the system,and in turn sustain the safety operation of the said system.As can be seen,we have defined and analyzed the connotation of the vulnerability of the urban infrastructure system based on the theory of vulnerability.Through a systematic literature review and a panel discussion,we have succeeded in identifying the influential factors of the system and categorizing the said factors from its internal and external aspects.In accordance with the actual necessity,we have set up an expert consultative group for the questionnaire inquiry with Delphi method.And,then,the relationship among the above said mutually influential factors has been preliminarily identified and determined through the statistical analysis of the results of the questionnaire.In addition,a hierarchical structure of the aforementioned influential factors and the urban infrastructure system vulnerability have been clarified and worked out based on the ISM model.The hierarchical structure of such factors demonstrates that the network topology,the physical condition and the network traffic can all be classified at the first level.The said three factors can be taken as the direct factors affecting the vulnerability of the system,which can all be attributed to the internal factors of the system,whereas the deliberate destruction and the system accidents should all be downcast to the second level.The two said factors can be attributed to the intermediate factors that affect the system vulnerability.As to the climatic change,the natural disasters,the government support,the economic and technical levels,the operation and management system in addition to the emergency rescue system should all be relegated to the third and fourth level ones.In one word,all the aforementioned 6 factors should all be taken as the root factors of the system vulnerability,belonging to the external factors and the operational management factors.Thus,it can be concluded that,keeping the stability of the internal factors and improving the management level of the system should all be taken into account the effective ways to reduce the system vulnerability.Hence,the given study enjoys certain theoretical and practical significance for understanding the vulnerability of the system and maintaining the safety operation of the urban infrastructure system.