The invention provides a method for gas purging through CO2-water alternating injection and application of the method. The method comprises the steps that CO2 is injected into a gas injection well, a producing well is closed, and the reservoir pressure is held to be high; and when the pressure of the producing well is restored to the original stratum pressure, the well is opened for production, and gas purging is conducted through CO2-water alternating injection. According to the method for gas purging through CO2-water alternating injection and the application of the method, through CO2-water alternating injection, the gas reservoir recovery efficiency can be improved, the purpose for retarding CO2 breakthrough is achieved, the problem that the design for the CO2-water alternating injection period is difficult is solved, and meanwhile the gas injection cost is reduced.