The invention provides a seabed natural gas hydrate mining device which mainly comprises a mining ship, a vortex tube, a gas mining tube, a gas mining casing tube and a collecting cover. High-pressure natural gas from a compressor enters the vortex tube, and the high-pressure gas is separated into cold fluid and hot fluid. The hot fluid directly enters a hydrate reservoir, solid hydrate is heated to be decomposed into natural gas, the natural gas enters the collecting cover through the gas mining tube to be collected, and the cold airflow is used for keeping the reservoir structure stable in the production process. Compared with the existing hydrate mining technology, the natural gas generated in the hydrate carrying-out process serves as a power source, it is not needed to consume additional energy, the advantages of being low in invested cost, low in running cost, environmentally friendly, efficient and the like are achieved, and wide application prospects are achieved in seabed hydrate mining.