The invention discloses a nano-metal composite and a preparation method thereof. The preparation method comprises the steps that a base material is provided, and hydrophilic groups are connected to the surface of the base material; surface modification is conducted on the base material through a silane coupling agent, and the base material with the silane coupling agent modified surface is obtained; the base material with the silane coupling agent modified surface, an initiator and a vinyl-containing polymer monomer are mixed, the vinyl-containing polymer monomer conducts a polymerization reaction, polymer brushes grow on the base material with the silane coupling agent modified surface, and the free-radical-polymerized base material is obtained; and PdCl4<2-> is made on the free-radical-polymerized base material in a displacing mode through ion exchange, then the base material is placed in a metal plating solution to conduct metal electroless deposition, and thus the nano-metal composite is obtained. The problems that in the prior art, the surface of nano-metal needs to be coated with a surfactant in actual use, consequently, the reaction activity of the nano-metal is not high, and the nano-metal cannot be recycled effectively are solved.