Deepwater natural gas hydrate exploitation system and method

The invention provides a deepwater natural gas hydrate exploitation system and method. The system comprises a straight well, porous radial wells which are divided into an upper group and a lower group and communicate with the straight well and extend in a natural gas hydrate reservoir stratum, a first packer, a second packer, a filling oil pipe and a withdrawing oil pipe, wherein the first packer and the second packer are arranged in the straight well and are used for packing a space in the well into a filling layer and a withdrawing layer; the upper group of radial wells communicate with the withdrawing layer between the first packer and the second packer; the lower group of radial wells communicate with the filling layer at the lower part of the second packer; the filling oil pipe and the withdrawing oil pipe are arranged in the straight well; the top end of the filling oil pipe is connected to a carbon dioxide filling system; the top end of the withdrawing oil pipe is connected to a natural gas collecting