The invention relates to catalysts for treating industrial waste water, in particular to an iron inner electrolysis catalyst and a preparation method thereof. The iron inner electrolysis catalyst comprises the following components: simple copper supported by molecular sieves, manganese dioxide supported by molecular sieves, and natural manganese ore with the mass ratio thereof being 1:0.5-1.0:0.5-1.0. The preparation method thereof comprises the following steps: respectively immersing roasted molecular sieves in the solutions of soluble copper salt and manganese salt by the supporting capacity of copper and manganese dioxide; dipping, drying and roasting the molecular sieves to respectively obtain the copper oxide and manganese dioxide supported by the molecular sieves; crushing and sieving the natural manganese ore to obtain the natural manganese ore granules; reducing the copper oxide supported by the molecular sieves by using hydrogen to obtain the simple copper supported by the molecular sieves; and mixing the simple copper supported by molecular sieves, manganese dioxide supported by molecular sieves, and natural manganese ore granules by the mass ratio to obtain the product.Accordingly, the invention is suitable for the pre-treatment before the biochemical treatment of high-chromaticity non-biodegradable industrial waste water.