Abstract: The dawsonite in oil-bearing reservoir was identified accurately with X-ray diffraction method for the first time in China,and its diffraction characteristics was given in detail.Research shows that the dawsonite in Hailaer Basin exists in both the eroded volcano tuff and sedimentary volcano tuff,and is paragenous with corrensite and allevardite frequently.This paragenetic association is one of the typomorphic minerals of eroded volcano tuff and sedimentary volcano tuff.The dawsonite in the Hailaer Basin forms by typical alkaline metasomatosis,because the volcano tuff is easily eroded under the alkaline conditions.The plagioclase alkaline metasomatosis by dawsonite results in the formation of the secondary porosity contributing to the hydrocarbon accumulation,which constitutes dominating oil-bearing reserver in some regions.