Abstract: According to the features of city gas pipeline network, this paper analyzes its running reliability, gives the assessment contents of reliability and proposes the classification principle of city gas pipeline network. The authors put all the process of pipeline management into three phases, that is, the beginning phase, the middle phase and the end phase. In addition, the probability method is applied to discuss the reliability for the beginning and the middle phase, and the failure tree of city gas pipeline network used in the beginning phase is presented. For the running safety of city gas pipeline network, the assuring measures are also brought forward.