Abnormally high formation pressure commonly exists in formation upper Es4, lower Es3, middle Es3 source rocks of Paleogene, Lijin subsag, Shengli oilfield. The formation mechanisms of abnormally high pore pressure in Paleogene source rocks are analyzed herein. Also, the pore pressure profiles of 80 drilled exploration wells in this subsag are established by Comprehensive Explanation Method. Moreover, the pore pressure distribution features of source rocks are researched through drawing contour maps of formation upper Es4, lower Es3, middle Es3, respectively. The Comprehensive Explanation Method has a high precision in calculating abnormally high pore pressure of source rocks in Lijin subsag formed with combined action of under-compaction and hydrocarbon generation. The abnormally high pore pressure of Paleogene source rocks in Lijin subsag distributes with a trend from northeast to southwest.The pore pressure is high or ultra-high in the central region of Lijin subsag, and decreases to a normal level in the periphery area. The abnormally high formation pressure in the source rocks of Lijin subsag is the main force of hydrocarbon expulsion from the central subsag to the periphery area.