The present invention provides an ultraviolet light based cleansing method and cleansing device. The method includes: (1) irradiating a substrate to be cleansed with ultraviolet light and controlling output energy of the ultraviolet light in order to control photon energy received by TFT component patterns formed on the substrate to be cleansed within an irradiation time period to be less than electron excitation energy that breaks down TFT component patterns; (2) cleansing the substrate to be cleansed with an alkaline solution; (3) cleansing the substrate to be cleansed with water/gas dual-fluid; (4) cleansing the substrate to be cleansed with deionized water; (5) drying the substrate to be cleansed with an air knife; and (6) subjecting the substrate to be cleansed to dehydration and drying to complete the cleansing operation, thereby improving product yield rate and cleanness.