Abstract: Various factors led to three leaking accidents of the natural gas pipeline in Maowusu Desert are analyzed and natural gas pipeline leaking fault tree is set up. By the fault tree model, 11 most trail collections of leaking fault tree system are obtained. Based on the qualitative analysis to its structural importance of elementary event, it is pointed out that among the essential factors, the fundamental factor of leaking accident is pipeline leaking other factors (A₁) and project safety and quality factor (A₂), the latter is the most important factor.