Abstract: In order to ascertain the oil?gas origin in Chepaizi area in northwestern margin of Junggar basin, this paper studied the 40 crude oil samples from the Miocene Shawan formation in Chunguang block of this basin using GC?MS analysis, and presented the distributions and compositions of aromatic hydrocarbons biomarker, as well as their geological and geochemical implications. There are abundant aromatic hydrocarbons detected in Shawan crude oil, which can be regarded as important basis for judgement of the organic matter maturity, kerogen type, hydrocarbon charge and migration direction. The study shows that the Shawan crude oil is in mature stage, formed in continental oil environment, and its kerogen contains a certain extent of imput higher plants, and there exist some defferences among them for different types of crude oils. According to the ratio index and m(4?MDBT)/m(1?MDBT), the Shawan crude oil in this area is originated from WS to ES directions, and characterized by that the light crude is close to hydrocarbon source area, with single oil source; the intermediate and heavyoils are relatively far from it, the former is mixed oil, the latter is highly degraded one