There are a lot of researches on qualitative aseismatic measures for buried gas pipeline crossing movable faults. But a few of them are quantitative, especially in the size and shape of the trench. The paper first established the finite element model of the strain of buried pipeline crossing a fault which effected by the size and shape of the trench. And it obtained new soil spring stiffness which considered different buried depth, bottom width of trench, trench slope and elastic modulus of soil. The mechanical analysis model of pipeline is established, and the limit state equation of pipeline is fitted. The reliability and sensitivity of the natural gas pipeline under fault action are analysed by a Monte Carlo method, and the error and accuracy are verified. When the pipeline is under tension, the sensitivity from large to small is buried depth, sand friction angle, pipe diameter, pipeline displacement, trench bottom width, trench depth, clay cohesion, trench slope and clay friction angle; when the pipeline is under pressure, the trench depth and clay cohesion have great influence. The findings of this study provide a reference for pipeline design and safety evaluation under fault action.