The Hulunhu Depression with thick deposits and well-developed strata is an important replacement exploration area in the Hailaer Basin .The Nantun Formation is its primary hydrocarbon source rock and the Tongbomiao and Damo -guaihe Fms are the secondary source rocks .These source rocks have supreme oil-generating conditions ,but no systematic study has been performed on its geothermal evolutionary history so far .The present geothermal gradient is 30.7℃/km in the Hulunhu Depression ,belonging to the moderate temperature field .The average paleogeothermal gradient recovered by the vitrinite reflectance , homogenization temperature of fluid inclusions and apatite fission track method is about 42-56 ℃/km,obviously higher than the present geothermal gradient .That is to say,the paleogeotemperature is higher than the present geotemperature .The paleogeotemperature reconstruction and geothermal history simulation showed that the Hulunhu Depression reached the maximum paleogeotemperature in the Late Yimin period (90Ma),and entered a cooling process since the Paleogene and Neogene .The maturity of the Lower Cretaceous hydrocarbon source rocks was mainly controlled by the paleogeothermal field .The results from the studies of the paleogeothermal evolutionary history and the authigenic illite dating of reservoirs showed that the Late Yimin period was a very important stage for hydrocarbon accumulation in the Hulunhu Depression .In this period , the depression uplifted and got denudated , the temperature of strata reduced ,the burial depth of source rocks decreased ,and the intensity of hydrocarbon generation weakened .%呼伦湖凹陷是海拉尔盆地油气勘探的重要接替区。该凹陷沉积厚度大，地层发育全，主要烃源岩层是南屯组，其次是铜钵庙组和大磨拐河组，生油条件十分优越，然而至今尚未对其热演化史进行系统研究。呼伦湖凹陷现今地温梯度为30.7℃／km，属于中温型地温场。根据镜质体反射率、包裹体测温和磷灰石裂变径迹法恢复呼伦湖凹陷的古地温梯度为42～56℃／km，大于现今地温梯度值，古地温高于今地温。古地温恢复及热史模拟表明，呼伦湖凹陷在伊敏组沉积晚期（约90 Ma）达到最高古地温，古近纪－新近纪以来是一个降温过程，下白垩统烃源岩热演化程度主要受古地温场控制。古地温演化史结合含油储层自生伊利石测年结果表明，伊敏组沉积晚期应该是呼伦湖凹陷一次非常重要的油气成藏期。伊敏组沉积晚期凹陷发生抬升剥蚀，地层温度降低，烃源岩埋深变浅，生烃强度减弱。
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