Abstract: The decomposition characteristics of C₄F₇N are related to buffer gas selection and solid material compatibility, and can also provide a reference for the fault identification of electrical equipment. Therefore, this paper first analyzes the dissociation path and main decomposition byproducts of C₄F₇N using the quantum chemical method. Then, C₄F₇N/CO₂ is taken as the object, and a series of experiments are carried out, including corona discharge, spark discharge, and suspension discharge. The influences of the mixing ratio and applied voltage on the type and content of decomposition byproducts are analyzed. The byproducts of C₄F₇N are CF₄, C₂F₆, C₃F₈, C₃F₆, 2-C₄F₆, 2-C₄F₈, i-C₄F₁₀CNCN, CF₃CN, C₂F₅CN and CF₂CFCN, and CO, CF₄ and C₃F₆ are the main byproducts. As the mixing ratio of C₄F₇N increases, the content of CO decreases, and the contents of perfluorinated hydrocarbon (PFCs) and nitriles increase. Since the suspension discharge relates to solid insulating materials, the contents of CO and CF₄ are higher than those of corona discharge and spark discharge. Finally, according to the formation and variation of the decomposition byproducts, this paper proposes the content ratios c(CO)/c(PFCs) and c(CF₄+C₂F₆)/c(C₃F₆) as the criteria to identify the typical discharge defects, which can provide a reference for fault identification and diagnosis of C₄F₇N/CO₂ gas insulated equipment.