The invention provides a new method and a device for producing synthetic natural gas. The method comprises continuous process flows of producing methane-rich gas containing over 94 mole percent of methane by using a coal gasification product as a raw material. The method provided by the invention does not use an expensive circulation compressor, reduces the operation cost and reduces the materialrequirements of a reactor, a waste boiler and a steam over-heater. The method has low requirement for catalyst operating temperature; a catalyst bed layer is not easy to cause temperature runaway andcan inhibit carbon precipitation so as to remarkably reduce the energy consumption of a methanation process; and the method has the advantages of reasonable process flows, operability, energy conservation and the like.