The invention discloses a device and method for purifying sulfur hexafluoride gas from sulfur hexafluoride mixed gas. The device comprises a mixed gas extraction pipeline, a buffer tank, a pressure maintaining valve, a mass flow controller, a first adsorption column, a second adsorption column, a storage tank and a nitrogen evacuation pipeline. The invention can achieve the aim of continuously purifying the SF6 gas through alternate operation and regeneration of the first adsorption column and the second adsorption column. The function of a first sulfur hexafluoride sensor and a second sulfurhexafluoride sensor is to find suitable adsorption and regeneration time, so that the first adsorption column and the second adsorption column can realize that the content of the SF6 in discharged N2is less than a discharging requirement stipulated in a relevant standard and can also enable the concentration of the desorbed SF6 gas in the regenerated adsorption columns to be 90 percent or more. The device is novel in design, simple in structure and convenient to operate; the SF6 in the SF6/N2 mixed gas in GIS equipment can be purified to be 90 percent or more, and then is recycled; the use amount of the SF6 is reduced, and the operation cost is reduced.