The invention discloses a method for synthesizing methane by utilizing oven gas. Product gas with methane concentration of more than 90 percent is obtained through the main steps of purifying to remove impurities, compressing to exchange heat, adding water vapor, first stage of methanation reaction, second stage of methanation reaction, third stage of methanation reaction, PSA methane separation and the like. By adopting the method and utilizing the oven gas as raw materials, synthetic natural gas with high content of methane, low content of impurities and high heating value can be obtained, which is favorable to protecting the environment, saving energy and developing new energy; in addition, in the method, the addition of appropriate water vapor in the raw materials of oven gas before the fist sage of reaction properly inhibits the depth of the methanation reaction, reduces the heat amount released in the whole reaction process, conduces the cooling of the gas after the reaction and prevents the occurrence of carbon deposition reaction to devitalize the activity of a catalyst, thus being beneficial to the continuous normal operation of the whole synthesizing process.