SF 6 can decompose under GIS partial discharge or overheating failure and a series of byproducts are generated, which declines the insulating strength of equipment. However, SF6 is inherently supposed to be more stable, and the possible reason for the degradation is the facilitation of metals such as Cu. To test this hypothesis, the surface reaction of SF 6 cleavage products with oxygen on Cu surface was calculated in this paper based on density functional theory. It was found that the activation energy for SF 6 dissociation is reduced owing to the interaction with Cu surface. The paper aims to explain the effect of the copper metal on the stability of SF 6 insulating gas.