Abstract: In order to comprehensively reveal the hydrocarbon generation and expulsion ability of source rocks of the Yanchang Formation in Xifeng area, Southwestern Ordos Basin, the authors investigates the maturity degree of source rocks in the Member 8 and 7 of Yanchang Formation which are closely related to the reservoir. pyrolysis analysis, dissolvable organic matter analysis, vitrinite reflectance of kerogen and biomarker parameter are applied in the research. The peak temperatures of Rock-Eval pyrolysis, conversion rates of bitumen and hydrocarbon, Ro values, OEP values, sterane parameter C29ααα-20S/(20S+20R) and hopane parameter C31αβ-22S/(22S+22R) all indicate that the source rocks in Member 8 and 7 are in the mature stage of organic matter and have reached the peak of hydrocarbon generation. Therefore the source rocks have provided with advantageous conditions to generating and expulsion of hydrocarbon. Although the structure position and buried depth of strata of different wells in Xifeng area are difference at present, the source rocks in Member 8 and 7 of Yanchang Formation have identical thermal evolution because of the similar subsidence history and thermal history. The study provides the basic information for wholly revealing the generating and expulsing ability of the source rocks in the formation.

Key words: Yanchang formation, source rock, thermal maturity degree, Xifeng oil field, Ordos basin 