The invention provides a method for producing methane from synthesis gas. The method comprises steps as follows: purified synthesis gas and a first methanation catalyst are subjected to contact reaction in a first methanation reactor and are continuously subjected to the contact reaction with a fresh/used first methanation catalyst and/or a regenerated first methanation catalyst in a second methanation reactor, high-temperature gas material flow is subjected to heat exchange cooling, and gas material flow I rich in methane is obtained; the gas material flow I and a second methanation catalystare subjected to the contact reaction in a third methanation reactor, gas material flow is cooled, and a gas product II rich in methane is obtained. According to the method, methane can be produced from the synthesis gas, furthermore, the moving-bed methanation catalysts can be regenerated and recycled online, so that strict requirements for feed gas pretreatment process are effectively reduced, meanwhile, the methanation catalysts undertake the function of a heat carrier in a moving bed, and reaction heat can be effectively utilized.