Disclosed herein is a method of coating a catalyst support, in which a monolithic catalyst support provided therein with a plurality of longitudinally formed channels is quantitatively coated with catalyst slurry applied to post-treatment of exhaust gas, including the steps of: introducing catalyst slurry into a quantitative container whose bottom is vertically moved; moving a catalyst support to the top of a container such that the bottom of the catalyst support and top of the container are horizontally disposed each other; sealing the bottom of the catalyst support and the top of the container from the outside; moving the bottom of the container upward; and applying a vacuum to the channels of the catalyst support.