The G Basin is a typical passive rift basin in Africa which growth formed by the influence of the shear zone of Central Africa. And the southern depression is the most important petroleum generative depression of the basin. In order tofurther clarify the exploration direction, need carry out the study of thegeothermal history andhydrocarbon accumulation. Reservoir temperature shows that the current average geothermal gradient is 3.9 ℃/100 re,belongs to the middle geothermal field. According to the vitrinite reflectance and inclusion thermometry, restored the thermal evolution history of southern depression. The study shows that the paleogeothermal gradient of the depression was 2.4 -3.77 ℃/100 m in Cretaceous and the paleogeothermal gradient is lower than today＇s. The paleotemperature recovery and thermal history modeling show that the maximum paleotemperature reached in the present day and the thermal evolution of Hydrocarbon source rocks in Lower Crataceous is mainly controled by present geothermal field. The study onhomogenization temperature of fluid inclusion shows that there were two fluid action events experienced in the southern depression of G Basin and they occurred at the early stage of Late Cretaceous （96.0 - 87.0 Ma） and Quaternary Period （3.0 -0 Ma）. The primaryhydrocarbon reservoir forming stages of Lower Cretaceous is the early stage of Late Cretaceous.
