The invention relates to a method for preparing a Ti-Si-N nano-coating and belongs to a method for preparing coatings for tool and mould. The method solves the problem of easy shedding of the coating in working conditions prepared by the existing method of reactive magnetron sputtering, and realizes metallurgical binding between a transition layer and the coating, thus improving the mechanical property of the coating. The method comprises the following steps of: (1) preheating; (2) sputter cleaning; (3) ion nitriding; (4) preparing the transition layer; and (5) preparing a surface layer. The method has the advantages of high production efficiency and low cost, the critical load Lc of the prepared coating and the substrate of a metal ceramic cutting tool is more than or equal to 65N, and the surface micro hardness HV is more than or equal to 3400. The method is suitable for manufacturing coating tools for low machinability materials, high speed dry-type milling stainless steel, iron-base super-alloy, high strength construction steel, wear-resistance cast steel, glass sealing alloy, and the like, and has good popularization and application prospect in manufacturing industries, such as automobile, aviation, space flight, resource equipment, and the like.