The utility model relates to a mix gas -insulated characteristic test device, including the seal box, set up in the seal box electrode pair put of position inside to and the temperature control system of the interior temperature of regulation seal box, be equipped with the gaseous inflation inlet that awaits measuring on the seal box, and be equipped with the barometer on the seal box, simultaneously the utility model discloses applied above -mentioned test device's mixed gas -insulated characteristic testing method is still provided. The utility model is used for it is experimental at the insulating properties under the gentle high low pressure state of height to the mist to acquire optimum gas ratio and the matching pressure of mixing of different temperature range gas -insulated equipment convenient and fast, optimize the severe cold district GIS gas -insulated design.