Abstract: The dolomite tight reservoir ofⅡoil layer of Xingouzui formation (Exl?Ⅱ) in Xingou area of Qianjiang sag is in low degree of exploration and research. This paper studied the crude oil geochemistry, oil source and genetic type in this reservoir, based on analysis data of the oil and hydrocarbon source rocks samples. The results show that the dolomite reservoir of Exl?Ⅱis of typical feature of tight oil reservoir, which is medium?low porosity, ultra?low permeability and super?small throat, and stronger potential of generating low?mature oil with high organic abundance and low thermal evolution of the muddy source rocks. The characteristics of the biomarkers indicate that the low?mature oil belongs to typical one from the saline lacustrine mudstone in source rocks of structural low, with both source and reservoir and short secondary migration. The parent materials of the oils are dominated by mixed types of organic matters including terrestrial higher plants, plankton and algae, etc. The early hydrocarbon generation of biological lipid is the main hydrocarbon?generating model for low mature oils in this area, while early degradation of sulfur?rich macromolecular could be its one of important models for hydrocarbon generation