The invention provides a preparation method for a modified lignocellulose ester-based Fenton-like catalyst and application of the catalyst to the field of wastewater treatment. The method comprises the following steps: drying and crushing cellulosic solid waste so as to obtain cellulosic solid waste powder; uniformly mixing the cellulosic solid waste powder with a modifier and an auxiliary agent; then adding a mixture obtained in the previous step into a mechanical activation solid-phase reactor and carrying out ball milling and a reaction; separating a product from grinding balls; adding a modified lignocellulose ester mixture obtained in the previous step into a solution of a ferric salt and/or ferrous salt under stirring; carrying out filtering; and drying filter residues so as to obtain the target catalyst. According to the invention, since the cellulosic solid waste and the like are used as raw materials, the waste is turned into the valuable and dealt with the waste, so recycling and high-value utilization of the cellulosic solid waste are realized; the preparation method employs a solid-phase method and is simple to operate; the added modifier and auxiliary agent do not need to separate, so waste gas, waste water and industrial residues are not produced, equipment investment is saved, and production cost is low; and the prepared catalyst can produce Fenton effect, has excellent water treatment effect, and is free of secondary pollution and applicable to a wide range of pH values.