Abstract: The Dalaoba Gas Condensate Field is a deep,high temperature,high pressure,high waxcontent and high condensate oil content reservoir in the Tarim Basin.Natural depletion production hasbeen carried out,and a large quantity of gas has condensed and remained in formation as condensate oil.Phase changes of injected gas and condensate oil in formation were studied.When injected gas metcondensate oil,interphase mass transfer took place due to dissolving and extracting effects,resulting inobvious changes of the composition and characteristics of petroleum system.Condensate oil in formationevaporated and the mobility of condensate oil was also improved.Expansion coefficient increased,viscosity and density decreased,and gas-liquid interfacial tension decreased.All these helped toimprove oil recovery rate.