Abstract: The study of oil-source rock showed that Jiuxi Depression developed two types of crude oils with different types of biomarker respectively, namely type I and type Ⅱ crude oils. Different biomarkers can indicate different parameters such as depositional environment, water medium, possible precursor organisms and heat maturity. The comparison of all parameters and their revealing geo-chemical meanings showed that type Ⅰ crude oil originally came from shale dolomitite developed in Xiagou Formation of the Lower Cretaceous,and type Ⅱ crude oil originally came from Chijinpu Formation of the Lower Cretaceous in Qinxi Sag.The comprehensive regional geology indicates that Chijinpu Formation of the Lower Cretaceous in Qinxi Sag is new source rock strata.