The invention discloses application of arsenic sulfide. Arsenic sulfide is used as a photocatalyst to degrade organic dye pollutants, thereby expanding the range of applications. The activity of arsenic sulfide in photocatalytic degradation of the organic dye pollutants, such as rhodamine B dye, is obviously higher than that of titanium dioxide P25 and is also higher than that of a high-activity Ag3PO4 photocatalyst. Arsenic sulfide disclosed by the invention has the advantages of high photocatalyst activity, simple preparation method and mild preparation conditions, and is conductive to popularization and application.