The present invention relates to a method for recovering methane gas by adding a gas mixture containing N2 and CO2 gases to natural gas hydrate and reacting them. The method for recovering methane gas from natural gas hydrate of the present invention comprises the step of replacing CH4 gas in natural gas hydrate with a gas mixture containing N2 and CO2 gases by adding the gas mixture to the natural gas hydrate. The method for recovering methane gas of the invention assures a recovery rate of CH4 gas much higher than prior art method without dissociating natural gas hydrate layer and utilization of flue gas as a gas mixture containing N2 and CO2 gases, which makes possible its practical application for the production of natural gas in terms of economy and environmental protection.