Abstract: The elastic 2phase method，combined with material balance equation，is used to calculate the whole well reserves.The method is mainly used in the pseduosteady state of gas reservoir production，the measurement of pressure and deliveralibility is precisely required，while the working system of gas reservoir exerts considerable influence on the reserves calculated with elastic 2phase method，the calculation reliability has been verified in practice，in early stage of development，the calculation accuracy of material balance equation is not high.Elastic 2 phase method combining with material balance equation is used to establish optimal multiple objective function，which can fully apply elastic 2 phase method，and express material balance.So，the method can be more widely used，the calculation result is more reliable and it can be greatly popularized in tight gas reservoirs.Case study indicates the method is resonable in theory，practical verification is operable.

Key words: elastic 2phase method, material balance equation, gas reservoir, single well reserves, multiobjective optimization