An inundation prevention system for a ship, the inundation prevention system comprising: an airbag part of 3D shape disposed in an installation area prepared in a hull; a fire-extinction gas ejection part configured to eject a fire extinction gas to the installation area but outside the airbag part; and an airbag actuation part configured to supply the fire extinction gas to the airbag part, if inundation occurs in the installation area, and to inflate the airbag part in the installation area for compulsory buoyancy, wherein the airbag part is formed corresponding to a 3D shape of the installation area, wherein the installation area comprises an equipment installation area including a multiplicity of facilities, and a passage area forming a move and escape path, wherein the airbag part is formed in a 3D shape distant from the equipment installation area and passage area in a specific interval, wherein the airbag actuation part comprises: a gas injection tube exposed to the installation area, connected with the airbag part, connected with the fire-extinction gas ejection part to form a flow line of the fire extinction gas, and equipped with a multiplicity of gas injection nozzles injecting the fire extinction gas into the airbag part; a shutoff valve installed at the gas injection tube and configured to open and close the flow line of the fire extinction gas; an actuation switch configured to open and close the shutoff valve; and a controller configured to receive a shutoff signal from the actuation switch, to drive the shutoff valve, compulsorily to inject the fire extinction gas into the airbag part connected with the gas injection part, and to inflate the airbag part. an airbag part of 3D shape disposed in an installation area prepared in a hull; a fire-extinction gas ejection part configured to eject a fire extinction gas to the installation area but outside the airbag part; and an airbag actuation part configured to supply the fire extinction gas to the airbag part, if inundation occurs in the installation area, and to inflate the airbag part in the installation area for compulsory buoyancy, wherein the airbag part is formed corresponding to a 3D shape of the installation area, wherein the installation area comprises an equipment installation area including a multiplicity of facilities, and a passage area forming a move and escape path, wherein the airbag part is formed in a 3D shape distant from the equipment installation area and passage area in a specific interval, wherein the airbag actuation part comprises: a gas injection tube exposed to the installation area, connected with the airbag part, connected with the fire-extinction gas ejection part to form a flow line of the fire extinction gas, and equipped with a multiplicity of gas injection nozzles injecting the fire extinction gas into the airbag part; a shutoff valve installed at the gas injection tube and configured to open and close the flow line of the fire extinction gas; an actuation switch configured to open and close the shutoff valve; and a controller configured to receive a shutoff signal from the actuation switch, to drive the shutoff valve, compulsorily to inject the fire extinction gas into the airbag part connected with the gas injection part, and to inflate the airbag part. a gas injection tube exposed to the installation area, connected with the airbag part, connected with the fire-extinction gas ejection part to form a flow line of the fire extinction gas, and equipped with a multiplicity of gas injection nozzles injecting the fire extinction gas into the airbag part; a shutoff valve installed at the gas injection tube and configured to open and close the flow line of the fire extinction gas; an actuation switch configured to open and close the shutoff valve; and a controller configured to receive a shutoff signal from the actuation switch, to drive the shutoff valve, compulsorily to inject the fire extinction gas into the airbag part connected with the gas injection part, and to inflate the airbag part.