Abstract: The SF₆ gas leakage fault occurred in the air chamber housing of a gas insulated closed combination switches. The causes of the leakage of the gas insulated switchgear housing were analyzed by means of macroscopic relationship, penetration detection, X-ray digital imaging detection, chemical composition analysis, mechanical property test, metallographic examination, scanning electron microscope and energy spectrum analysis, finite element simulation analysis. The results show that the content of Al and Si elements in the local area was high. During the casting process, the housing material produced loose and porosity defects, and the defects were not completely removed during the repair welding. Under the combined action of internal medium stress and welding residual stress, the housing cracked and produced penetrating defects, which eventually led to leakage failure of the housing.