On the basis of illite dating method, hydrocarbon generated and hydrocarbon expulsed process and homogenization temperatures of fluid inclusion, the formation stages of oil-gas reservoirs in Hailaer Basin were studied. The results show that there are two main formation stages of oil-gas reservoirs in Hailaer Basin. The first stage is about 120~80 Ma, which is corresponding to the sedimentary period of Yimin Formation-early sedimentary period of Qingyuangang Formation, and it is the main formation time of oil-gas reservoirs in Hailaer basin.