The invention provides a combined tower type methanation apparatus and a methanation process. The methanation process comprises the following steps that: feed gas exchanges heat with high-temperaturegas via a winding heat exchanger II, then enters a winding heat exchanger I for heat exchange and then undergoes a methanation reaction in an isothermal catalyst bed I so as to form high-temperature gas I; the high-temperature gas I is cooled by the winding heat exchanger I and then enters a heat-insulation stationary catalyst bed I, and reacted high-temperature gas is cooled and then enters an isothermal catalyst bed II so as to form high-temperature gas II; the high-temperature gas II is cooled by the winding heat exchanger II and then enters a heat-insulation stationary catalyst bed II, then continuous cooling is carried out and gas-liquid separation is conducted via a gas-liquid separator I, and a gas phase enters the winding heat exchanger II for heat exchange with high-temperature gas and then enters a supplementary methanation reactor; and reacted process gas successively passes through a boiler feed water preheater III, an air cooler, a water cooler and a gas-liquid separator II so as to separate a product, i.e., natural gas. The process provided by the invention has higher economic benefits, lower comprehensive energy consumption and smaller equipment size.