The invention discloses a device for measuring the concentration of sulfur dioxide in sulfur-hexafluoride (SF6) decomposition gas and a measuring method thereof and belongs to the technical field of photoelectric-technology detection. The invention aims at solving the problems of slow corresponding speed and low measurement accuracy in the existing device and method for measuring the concentrationof the sulfur dioxide in the SF6 decomposition gas. The measuring method comprises the following steps: introducing atmosphere and the SF6 decomposition gas into a sample cell respectively in sequence, controlling a 1350cm<-1> laser to emit laser with the waveband of 1350cm<-1> by using a laser controller, obtaining the spectrum of the atmosphere and the spectrum of SO2 absorbed by the laser withthe waveband of 1350cm<-1> in sequence according to a spectrometer, and then obtaining the concentration of the SO2 gas introduced into the sample pool by utilizing the beer's law finally. The deviceand the measuring method disclosed by the invention are used for measuring the concentration of SO2 gas in the SF6 decomposition gas.