To research the performance of gasbag used in bladder-type dispersal system, the fluid-structure interaction (FSI) model is established to simulate the inflating process of the metal gasbag (304 stainless steel) with a initially flat form. Then the dynamic response of bag's deformation and the changing law of internal flow field are acquired, and the results show a good agreement with the experimental results. Besides, the performances of gasbag with the change of its geometry and inlet conditions are investigated. The results show that the inlet diameter of gasbag and the inlet conditions are the key factor influencing the bullet's separating speed and overload. The larger the inlet diameter or the charge weight is, the greater the bullet's overload is. And when the bag's inlet diameter is different, there is an existence of the extreme separation speed of bullet with a certain amount of charge. The bag's initial area has a small impact on the change of speed (the difference is only 4%), while it affects the magnitude of the pressure of gas in the gasbag obviously. The larger the area, the smaller the pressure presents, which is beneficial to reducing the stress level of the wall of gasbag. So the calculation results can provide a mainly reference for the optimal design and engineering application of gasbag.