Abstract: Based on detailed pre-treatment works of hydrocarbon rocks in the Upper Triassic of Western Sichuan Depression of Sichuan Basin,organic geochemistry features are analyzed.Hydrocarbon source rocks have high organic matter abundance in total.Organic matter is mainly humosapropelic,and is during the mature and post mature evolutionary phase.Studies have shown that expulsion intension can ultimately materialize the quality of source rocks.In this paper,based on expulsion intension,the study area has been divided into 3 categories.Type Ⅰ locates in Shifang,Pengzhou,Wenjiang,Dayi and Dujiangyan,covering about 5 412 km².The hydrocarbon source rock thickness is about 1 000-1 650 m,and the expulsion intension is about(100-270)×10⁸m³/km².Type Ⅱ locates in Mianyang,Mianzhu,Zhongjiang and Chengdu,covering about 6 281 km².The hydrocarbon source rock thickness is about 700-1 500 m,and the expulsion intension is about(50-100)×10⁸m³/km².Type Ⅲ locates in Anxian,Fenggu and Longquanyi,covering about 4 895 km².The hydrocarbon source rock thickness is about 400-700 m,and the expulsion intension is about(10-50)×10⁸m³/km².