Abstract: In order to establish a method for quantitative analysis of the purity of gaseous Uranium hexafluoride using Fourier infrared spectroscopy under low pressure, the absorption peak at 1 150 cm^-1 was selected as the characteristic absorption peak for quantitative analysis of the purity of uranium hexafluoride. It was showed that the pressure of gas analysis has a direct effect on the area of characteristic peak under low pressure condition, which could not be ignored in the process of purity calculation. Aiming at the online analysis demand of the residual UF₆ in the tail material after UF6 gas was purified, the gas standard UF₆ samples with different purity and pressure conditions were analyzed by establishing an infrared analysis system, a standard sample ratio system and a background spectrum calibration device that could meet the requirements of vacuum sealing. The calculation formula for the relationship between the UF₆ purity and its characteristic absorption peak area as well as the gas absolute pressure were established. The experimental results showed that the purity of gaseous UF₆ which was in the pressure range of 60~140 Pa and the purity range of 0~100% could be accurately analyzed by this method.