The invention discloses a gas inflation device of sulfur hexafluoride and nitrogen mixed gas and an operation method of the gas inflation device. Four ports of a four-way valve set communicate with agas inflation unit, a to-be-inflated electric power equipment cavity, a gas state parameter detection unit and a gas uniform buffering unit correspondingly. The gas inflation unit comprises an SF6 gasdistribution branch, an N2 gas distribution branch and a feedback control adjusting module. A gas outlet of the SF6 gas distribution branch and a gas outlet of the N2 gas distribution branch communicate with the gas inlet of the feedback control adjusting module. The SF6 gas distribution branch and the N2 gas distribution branch comprise gas storage bottles, pressure reducing valves, gas pressuremeters and gas flow control valves. The gas state parameter detection unit is used for detecting the gas pressure and mixing ratio of mixed gas in the to-be-inflated electric power equipment cavity.The gas uniform buffering unit comprises a compressor and a buffering tank. The gas inflation device is a portable gas inflation device, is high in mixing ratio control precision, and can reduce the time required by mixing the mixed gas.