The gas insulated switchdear(GIS) is a mechanical switching device that connects and breaks current circuit to protect the electric equipment in a power network. To maintain the highest insulation level, main parts of the GIS were placed in the tank with insulating gas under the prescribed design pressure. According to IEC62271-203, it is necessary that tank should have strength to endure the pressure of the proof test which reaches many times of the design pressure to consider rapid increase of the internal pressure and the possible valiability of manufacturing process of the tank. For this reason, it is very important to predict the burst pressure of the tank to design the AC4CH-T6 casting aluminum alloy tank of GIS appropriately. In this study, a fracture criterion was proposed to predict tha fracture response of the AC4CH-T6 casting aluminum alloy by conducting a series of tests. By using the fracture criterion of the AC4CH-T6 and Finite Element Analysis(FEA), the burst pressure of actual tanks was proposed. Finally, the validity of predicted burst pressure of the tank was evaluated by compaing results from the actual hydaulic test of the tank.