The invention discloses a seabed natural gas collecting device using hot water in built-in buoyancy tanks for wall surface heating, belonging to the technical field of natural gas collection. The seabed natural gas collecting device comprises a mother ship; the mother ship is provided with a natural gas collecting and storing unit; the natural gas collecting and storing unit is connected with the top of a natural gas collecting cover through a gas extracting pipeline; the natural gas collecting cover is connected with the bottom of the mother ship through a waterproof pipe; the gas extracting pipeline is arranged in the waterproof pipe; the periphery of the bottom of the natural gas collecting cover is provided with an anchoring system; the bottom of the natural gas collecting cover is provided with a pressure adjusting system; the outer wall of the bottom of the natural gas collecting cover is provided with a propulsion system; the sidewall of the natural gas collecting cover is provided with a density adjusting system; and a temperature adjusting system and a stirring system are arranged in the natural gas collecting cover. The seabed natural gas collecting device mainly overcomes the problems of loss and leakage of natural gas in decomposition, collection and exploitation of natural gas hydrate in a seabed.