The invention discloses a gas mixture filling device of high-voltage electrical equipment in an extremely cold area. The gas mixture filling device comprises a gas-filling device temperature-regulating box and a gas filling device body arranged in the gas-filling device temperature-regulating box; the gas-filling device temperature-regulating box is provided with a temperature regulating device; the gas filling device body comprises an SF6 gas filling pipeline, a CF4 or N2 gas filling pipeline, a mixed gas cylinder and a ratio flow control device; an output opening of the SF6 gas filling pipeline and an output opening of the CF4 or N2 gas filling pipeline communicate with an input opening of the mixed gas cylinder; the SF6 gas filling pipeline sequentially comprises an SF6 gas tank interface, a high pressure reducing valve, a first proportional solenoid valve, a first manually-operated valve and a first mass flow controlling instrument from an input opening to the output opening; the CF4 or N2 gas filling pipeline sequentially comprises a CF4 or N2 gas source tube interface, a second proportional solenoid valve, a second manually-operated valve and a second mass flow controlling instrument from an input opening to the output opening; and the mixed gas cylinder is provided with an output pipeline for being connected with the high-voltage electrical equipment. The gas mixture filling device of the high-voltage electrical equipment in the extremely cold area has the characteristics of being constant in gas supplying pressure, safe, reliable, resistant to low temperature and the like.