This paper deals with distribution of source rock, type, abundance and maturity of organic matter of the Lower Member of the Paleogene Yuanjiang Formation in the Yuanjiang Depression. The study indicates that area of the source rock is about 1 383 km² with a thickness of 50~125 m and average thickness of about 80 m. Good source rock is distributed over east and west depression centers. Organic matter belongs to humic and sapropel type. The source rock is in mature stage on the basis of vitrinite reflectance, sporopollen analysis and so on.