In recent years, many scholars have been devoted to the search for environmentally friendly gas-insulated medium to gradually replace robust greenhouse gases, such as sulfur hexafluoride (SF6), which are widely used in the power industry at this stage, and thus promote the green development of power industry. In this study, the decomposition characteristics of C5-PFK (C5-perfluoroketone), a potential environmentally friendly alternative gas, were theoretically investigated. First, the bond order and Fukui functions of C5-PFK were calculated based on density functional theory, and the reactivity and stability of C5-PFK were revealed from a molecular viewpoint. Second, the decomposition characteristics of C5-PFK/CO2 gas mixture were examined through reactive molecular dynamics theory. The decomposition mechanism of C5-PFK/CO2 gas mixture and the yield and distribution of the main decomposition products at different temperatures and mixing ratios were obtained. Results show that chemical bonds between carbonyl and its linked carbon atoms in C5-PFK molecule are weak but with robust reactivity. C5-PFK/CO2 gas mixture decomposes mainly above 2600 K, producing CF3 center dot, CO, C3F7CO center dot, CF center dot, CF2 center dot, C3F7 center dot, F-center dot, CF3, and C-center dot, among which the CF3 center dot and CO contents are the highest. The decomposition characteristics of the gas mixture with a larger content of C5-PFK are inferior to those of the smaller content under the same condition. Relevant research results provide guidance for further clarifying the electrical characteristics, such as self-recovery and arc suppression performance of C5-PFK/CO2 gas mixtures and engineering applications.