Trace O-2 significantly affects the diagnosis accuracy of decomposed components analysis method for spark discharge due to its direct participation in SF6 decomposition process. Therefore, spark discharge decomposition experiments were conducted under different proportions of SF6/O-2 mixtures. The influence rules and mechanisms of phi(O-2) on the content and characteristic ratio of SF6 spark discharge decomposed components were analysed quantitatively. Meanwhile, the materials on the electrode surface after spark discharge were conducted XPS analysis. Results show: no matter how much O-2 adds, there exist SOF2, SOF4, SO2, and SO2F2 in the process of SF6 decomposition. The increase of phi(O-2) plays a positive role in the production of SOF4 and SO2F2, but has the adverse effect on SO2. The content of SOF2 barely changes with phi(O-2) increasing. Characteristic ratio phi(SO2F2 + SOF4)/phi(SOF2) gradually grows with phi(O-2), but change little with discharge time extended. The X-ray photoelectron spectra show that the solid materials on the surface of the plate electrode after discharge contain Al2O3 and AlF3, and S mainly exists as metal sulfides.