It has been proven that the gas trifluoromethanesulfonyl fluoride (CF3SO2F) has good dielectric performance and potential to replace strong greenhouse gas sulfur hexafluoride (SF6), which is the most commonly used insulating gas in electrical engineering area. In this paper, acute toxic gas inhalation test was carried out. The results showed that the lethal concentration 50% (LC50) for female rats was 27.1 g/m3 and 23.3 g/m3 for male rats. The behavioral and vital sign changes in the rats were recorded. Pathological sections of the main organs revealed that the heart, lungs, spleen and eyes suffered the most damage from the gas. This research also provides scientific suggestions for the protection in practical engineering.