Abstract: The oil pool in the metamorphosed basement in Yaerxia was discovered in 1959. Its reservoir rock is composed of an interbed of slightly metamorposed greyish-green and purple sandstone and arenaceous shale of Silurian. Oil accumulations lie in the neighborhood of faults or at the intersection of faults and on the anticlinal axis where fractures are well developed. The overburden consists of sections in Silurian with no fractures and mudstones of Cretaceous and Tertiary. Crude oil comes from the lower Xinmingbao group of Cretaceous in the Qingsi depression, with properties similar to that from the other pools in the western part of the Jiuquan basin-paraffin-naphthenic hydrocarbons. On the plane, the oil pool is distributed like a sheet, and in the vertical section it is divided into multiple zones. Simultaneous with the study of the area covered by the oil pool, efforts should be directed to find out the lower depth limit of the pool so as to discover more reserve.