The invention discloses a calculation method for dynamic reserves of gas reservoir. The calculation method aiming at solving the problems that an existing gas reservoir dynamic reserve calculation method is lack of information, harsh in use conditions or complicated in analysis process, the calculation method is based on the advantages of a
material balance method and is combined with the gas seepage process, a vertical
pipe flow model, a gas well productivity equation and a
material balance equation. The calculation method comprises the following steps that S1, production
dynamic data are prepared; S2, the bottom hole flowing pressure is calculated, specifically, the bottom hole flowing pressure of a gas well is calculated according to the processed production
dynamic data of the gas well; S3, the formation static pressure is calculated, specifically, a binomial deliverability equation of the gas well is adopted to calculate the average formation pressure of the gas well; S4, flow stages are divided, specifically, a boundary
control flow stage, an unstable flow stage and a
transition stage are determined; and S5, the dynamic reserves are calculated, specifically, the dynamic reserves after the unstable flow stage of the gas well is finished is calculated, and the dynamic reserves is added to the cumulative gas production in the unstable flow stage to get the true dynamic reserves of the gas well.