Abstract: Based on the restoration of the paleo-burial history and paleo-anormalous pressure of natural gas seals,the effectiveness of natural gas seals in western part of the southern fringe of the Junggar Basin has been evaluated combined with the hydrocarbon-generating and hydrocarbon-discharging time of major source rock.It is considered that the Anjihaihe Formation is the effective caprock for the Jurassic source rock,and the Sangonghe Formation and the Baijiantan Formations are effective for the Middle Permian one.