Atmospheric water vapor exhibits strong spectral features in the far-IR region，particularly below 400 cm-1.Therefore,water vapor absorption bands may severely obscure important sample features in a far-IR spectrum.In this article,humidity compensation was applied to remove water vapor bands during the acquiring process of a far-IR spectrum.The scanning procedure of a single-beam sample spectrum was divided into two stages.At the first stage,the appearance of water vapor peaks is allowed and the absorption direction and intensity of water vapor bands can be observed easily at the end of this stage.Then,the relative humidity in the sample compartment of the spectrometer has to be changed by a dry or a wet air supply depending on the absorption direction of water vapor bands.For example,if the absorbance of water vapor is negative at the end of the first stage,then a wet air supply is necessary.After the relative humidity changes to a certain extent,water vapor peaks will become smaller and smaller with the increase in scanning number during the second stage.By this way,water vapor noise can be removed progressively and completely at last.