Abstract: Provided a method for in situ synthesizing ultrafine and highly loaded Ag NPs on the surface of tannin-coated phenolic resin microspheres, the method comprises: (1) preparing phenolic resin microspheres by hydrothermal solvent method; (2) stirring a mixed phase of the phenolic resin microspheres and a tannin solution under a alkaline condition at room temperature to obtain tannin-coated phenolic resin microspheres; (3) adding the tannin-coated phenolic resin microspheres to a silver ammonia solution to obtain a composite that being loaded with Ag NPs on the surface of tannin-coated phenolic resin microspheres. Ag NPs in the composite are ultrafine and highly loaded. The raw materials of the method are low price, and the preparation process is extremely simple and environmentally friendly. In addition, the tannin coating technology is also suitable for other nanomaterials, such as SiO2, TiO2 and Fe3O4, etc., and has good application prospects and market potential.