The photochemical degradation mechanisms of an azo dye Direct Red 4BS and Methyl Orange on hematite in the presence of H2O2 were investigated. The decolorization of azo dyes was attributed to the forming surface complex between specific bond of the dyes and hematite, which facilitate the electron transfer from hematite to azo bond. No mineralization of azo dyes occurred in the presence of visible irradiation, only chromogenic group destroyed in the photo-chemical reaction process. Surface complex between azo dyes and hematite will be destroyed under alkaline solution which suggested the active site or the formed surface complex had been destroyed by OH–. Chemical adsorption of the azo dyes on hematite was critical factor which affect the decolorization efficiency of the photoreaction.