The gaseous fire Suppression system (GFSS) has excellent features such as equipments can be restored early after fire accident. So the system rapidly spreads recently. The purpose of the present study is to develop the simulator of GFSS by bond graph that is often used for dynamic characteristic analysis of the hydraulics and pneumatics system. In this study, a gas cylinder, pipe, a protection room and a pressure relief duct are expressed by the bond graph and the injection of the extinction gas into the protection room is simulated. The result of the simulation is compared with that of the experiment, which shows good agreement. It is also clarified that the maximum indoor pressure greatly exceeds the pressure obtained from the conventional design method.