Abstract: Based on the reliability concept of gas pipeline network, the maximum flow reliability in the graph theory and threshold level-based unit importance are introduced into the analysis of reliability of dendritic gas pipeline network system in order to obtain a mathematical model for resolving reliability as the reliability indicator of gas pipeline networks, which is used to evaluate the reliability of gas pipeline network system. Combined with the gathering network case, No.10 well field in Sulige Gasfield, Sudan, specific application steps of this method are elaborated, and the main factors affecting the reliability of pipeline network systems are analyzed. It is pointed out that the correctness of reliability calculation for pipeline network systems strongly depends on the accuracy of reliability data of units constituted the systems. The impacts of pipeline network topological structures and importance of pipe section units on reliability of pipeline network systems are larger, and the pipe section closer to the convergence point is subject to the higher unit importance. The expression of the threshold levelbased unit importance in the reliability of pipeline network systems is not perfect and other reliability indicators are required. When the plan for gathering pipeline network is selected, process availability, economy, program reliability and other factors shall be considered comprehensively.