Abstract: Fracture occurred in the thread relief groove root of charging valve shell of a type of gas supply devices applied to helicopter connected to the cylinder shell. The charging valve shell was produced by aluminum alloy 7A09, T6 state. A study was conducted by means of fracture analysis, chemical composition analysis, metallographic examination, hardness testing, and combined with the storage, use and fracture conditions of gas supply devices. The results showed that the fracture of charging valve shell was attributed to the stress corrosion. According to the experiment results, measures had been suggested to prevent such failure.