Determination of the influence and mechanism of metallic materials on SF6 decomposition under direct current (DC) partial discharge is one of the key aspects to improve SF6 decomposition component analysis (DCA). In this study, three kinds of metallic materials, namely, aluminum, copper, and 18/8 stainless steel, were made into needle-plate electrons, and then used in the SF6 positive DC partial discharge decomposition experiments. The influences of metallic materials on the five main decomposition components (i.e., CF4, CO2, SOF2, SO2F2, and SO2) were determined by gas chromatography-mass spectrometry. Results showed no significant correlation among the contents of CO2 for the different kinds of metallic materials. However, the metallic materials considerably influenced the contents of the other four gases. The difference in SF6 decomposition characteristics for the different metal electrodes was mainly due to the difference in anti-halogenation ability of metals and the passive film. Therefore, the impacts of different metallic materials should be considered when using SF6 DCA for the condition monitoring and fault diagnosis of DC gas-insulated equipment.