The invention discloses a built-in floating box spiral pipeline gas heating type seabed natural gas collecting device and method, and belongs to the technical field of natural gas collection. The seabed natural gas collecting device comprises a mother ship and a hollow natural gas collecting hood, and the mother ship is provided with a natural gas storing device and a pressure supply module. The natural gas storing device is connected with the top of the natural gas collecting hood through a gas extraction pipeline, the natural gas collecting hood is connected to the bottom of the mother ship through a marine riser, and the gas extraction pipeline is arranged in the marine riser. An anchoring system is arranged on the periphery of the bottom of the natural gas collecting hood, a pressure adjusting system is arranged at the bottom of the natural gas collecting hood, and a temperature adjusting system and a stirring system are arranged in the natural gas collecting hood. A propelling system is arranged on the outer wall of the natural gas collecting hood. A density adjusting system is arranged in the side wall of the natural gas collecting hood. By means of the seabed natural gas collecting device and method, the purpose that natural gas cannot dissipate and leak in the decomposition collecting and exploiting process of natural gas hydrates on a seabed mud bed is mainly achieved.