The invention relates to the technical field of marine hydrate accumulation mining, and discloses a return-type well structure and method for geothermal exploitation of marine hydrate accumulation byutilizing terrestrial heat. The structure adopts a return-type well structure, utilizes a heat-carrying fluid to transfer the energy of the geothermal layer to the hydrate layer to promote the decomposition of the natural gas hydrate, which can realize the recycling of the heat-carrying fluid while enhancing the heat conduction efficiency, and the structure has the advantages of fast mining speed,low mining cost, low energy loss, high heat utilization.