Abstract: Based on the comprehensive study of the available outcrop and geophysical data of Tostai area, it is concluded that; 1)Tostai ,a basement platform on the top of the front monocline of the Tianshan mountains, was formed by the northwestward dextral strike slip movement of the western North Tianshan Morntain in Himaiayan period; 2)There are three rows of anticlines on the basdment platform: The southern row of anticiines wcre deformed by several structural movements and accompanted by south- dipping Mesozoic normal faults; the middie and the northern rows were formed during Himalayan movement and are thin-skinned structures resulted from north-dipping back thrust faulting ,3)The oil and gas seepage in Tostai was migrated from Sikeshu depression in the north in late Himalayan period;4 )The frontal structures are the most prospective exploration targets. The anticlinal , the fault-blocked and baserock reservoirs may be penetrated by one vertical well.

Key words: Southern margin of Junggar Basin, Tostai uplift, Sikeshu deptession, Back thtust, Petroleum exploration