Wuerxun depression is a sag with a high degree exploration in the south of Hailaer basin, Inner Mongolia. It is the main oil-gas-bearing depression in which the deposit thickness is big, and the stratum grows entirely, and the oil-generating condition is very superior. The main source rock is Nantun Formation, and the next is Tongbomiao Formation and Damoguaihe Formation. The average paleogeothermal gradient recovered by the fission track method is about 3. 44 ℃/hm, which is close to present geothermal gradient (3. 3 ℃/hm). The results of paleotemperature and thermal history simulation show that Wuerxun depression has been undergone a heating process since Mesozoic Era, and the maturity of the source rock is controlled by present geothermal field. The geothermal history and illite dating results reveal that the formation of oil-gas reservoirs have two stages in Wuerxun depression, which are in the late period of Early Creaceous and since Tertiary, and the late period of Early Creaceous is the main stage, and the second stage is since Tertiary. The source rock began to generate oil and gas in a second peak since Tertiary. The second stage is important for the formation and concentration of oil-gas reservoirs in Wuerxun depression.%乌尔逊凹陷是内蒙古海拉尔盆地内勘验程度较高的一个南部凹陷,该凹陷沉积厚度大,地层发育全,生油条件十分优越,是海拉尔盆地主要产油气凹陷.主要烃源岩层是南屯组,其次是铜钵庙组和大磨拐河组.根据磷灰石裂变径迹法恢复的乌尔逊凹陷早白垩世古地温梯度为3.44℃/hm,接近现今地温梯度3.3℃/hm.古地温恢复及热演化史模拟表明,乌尔逊凹陷中生代以来经历了一个升温过程,下白垩统烃源岩热演化程度主要受现今地温场控制.热演化史与油气关系研究结合伊利石测年结果表明,乌尔逊凹陷油气成藏期主要有两期,为早白垩世晚期及古近纪以来,且以早白垩世晚期为主要成藏期；古近纪以来为第二期成藏阶段,烃源岩进入第二次生油高峰期.第二次成藏时期对乌尔逊凹陷油气藏的形成起着重要作用,是制约油气富集的重要因素.
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