The invention provides a middle-high voltage electrical equipment insulation and arc extinguishing medium and a selection method thereof. The insulation and arc extinguishing medium is a perfluoro ketone mixed gas; and the perfluoro ketone mixed gas has high insulation strength and a low greenhouse effect, so that the perfluoro ketone mixed gas can replace sulfur hexafluoride to serve as a new-generation gas insulation and arc-extinguishing medium, and can be widely applied to high-voltage electrical equipment, such as gas insulation transformers, gas insulation combined electric appliances, gas insulation power transmission pipelines and the like. The selection method provided by the invention is simple, and proportions of the insulation and arc-extinguishing medium suitable for differentmiddle-high voltage electrical equipment at different ambient temperatures can be efficiently selected, so as to obtain the insulation and arc-extinguishing medium with the optimal comprehensive performance.