Abstract: During nuclear facility decommission under construction, it is very important for workers to wear respirator to avoid harm of Am aerosols. So the protection effect of respirator is very important. The protection effect of respirator was calculated and evaluated according to the data achieved from engineering practice. The result shows that the protection effect is better than target management value and the respirator is effective to protect workers from harm of Am aerosols. The respirator is applied to other nuclear facility decommission.