In order to recognize partial discharge by analysis of SF6 decomposition products, the decomposition characteristic of SF6 under different partial discharges should be investigated, and also the feature parameters of decomposition products should be found. The decomposition of SF6 is simulated under partial discharge generated by needle defect and contamination defect respectively on the SF6 decomposition equipment made especially for the experiment. Three kinds of byproducts namely CF4, SO2F2 and SOF2 are detected, and their concentration changes with time are also studied. After that, the characteristics of three kinds of concentration ratios namely SOF2/SO2F2, SO2F2/CF4 and SOF2/CF4 under two defects are analyzed. The results show that SOF2, SO2F2 and CF4 exist in the byproducts under both the two defects. Moreover, the increase rules of the three kinds of byproducts under two defects are obviously different. Meanwhile the results illustrate that the three contamination ratios under the two defects have a notable disparity. Therefore the concentration ratios of the decomposition products can be used as feature parameters for partial discharge recognition.