Abstract: A hypochlorous acid preparation system is provided. The hypochlorous acid preparation system includes: a hypochlorous acid preparation apparatus comprising: a first inlet, wherein sulfuric acid collected from a clean room located in a semiconductor fabrication plant enters the hypochlorous acid preparation apparatus through the first inlet; a second inlet, wherein sodium hypochlorite solution enters the hypochlorous acid preparation apparatus through the second inlet; a third inlet, wherein deionized water enters the hypochlorous acid preparation apparatus through the third inlet; and an outlet, wherein hypochlorous acid is produced in situ by mixing the sulfuric acid, the sodium hypochlorite solution, and the deionized water and exits the hypochlorous acid preparation apparatus through the outlet.