To resolve the pollution problems of the aircraft pylon which is caused by the agents combustion insufficient when the throwing bomb working, we provide a closed cavity high pressure gas welding technology with flammable and explosive agents. According to the needs of the product process and the reality of the welded product, the resistance welding principle and the related methods are introduced and the inflation methods, welding methods and welding strength and safety are analyzed and tested. The high pressure automatic welding device is designed to realize automatic welding. The results show that the operation is simple, safe, reliable, fast and efficient.