Abstract: Jiyang Depression is an important exploration area in Shengli Oilfield.It is very important to de-cide its paleotemperature for the study of hydrocarbon generation history and pool forming history.Through integrated study of crystallinity of authigenic illite and chemical constitution of authigenic chlorite,it is concluded that the Cenozoic paleogeothermal gradient is from 37.2℃/km to 38.2℃/ km and it is also proved this is an effective way to study the basin thermal history.