Abstract: JZ)The second member of Liushagang formation is the principal layer of source rocks in Weixinan sag,it is very important to research into the organic facies of source rocks of the second member of Liushagang formation.According to the analysis of sedimentary environment、geochemical characteristics and biological sources,the source rocks of the second member of Liushagang formation in Weixinan sag is divided into middle-deep lake algal source organic facies、middle-deep lake commix source organic facies、littoral and shallow lake commix source organic facies and fan delta commix source organic facies.The middle-deep lake algal source organic facies,widely and thickly distributed,rich in organic matter,with kerogen type of Ⅰ-Ⅱ₁,is the main source rock of the Weixinan sag,and makes great contribution to oil and gas accumulation;Littoral and shallow lake commix source organic facies,widely and thickly distributed,rich in organic matter,with kerogen type of Ⅱ₁-Ⅱ₂,is the major source rock of the Weixinan sag.