Abstract: Three sets of source rocks developed upwards in the Eocene Niubao Formation in the Lunpola Basin, i.e., the middle part of the second member of Niubao Formation (E₂n₂²), the upper part of the second member of Niubao Formation (E₂n₂³), and the lower part of the third member of Niubao Formation (E₂n₃¹). Based on drilling, seismic and hydrocarbon fluid inclusion analyses, the thermal evolution history of the basin and the maturity history of source rocks in the Niubao Formation were systematically analyzed with basin simulation technology. From the E₂n₃ to the third member of the Oligocene Dingqinghu Formation, the paleogeothermal gradient in the Lunpola Basin consistently decreases from 66.7 to 40℃/km, showing the characteristics of a typical heating basin. The growth of paleogeothermal gradient is clearly related to regional tectonic uplifting. The source rocks in the E₂n₂² and E₂n₂³ became mature early and have a higher maturity. They entered oil generation thresholds during the middle-late Eocene (46.4-37.5 Ma) and early Oligocene (36.6-33.5 Ma), respectively. At present, they are mature and generating oil (R_o=0.7%-1.3%), and serve as the main source rock in the study area. At present, the thermal evolution extent of E₂n₂² and E₂n₂³ hydrocarbon source rocks in the Jiangriacuo Sag in the west is the highest, and its hydrocarbon forming and supplying ability is superior to the Jiangjiangcuo and Pacuo sags in the center and east.