The invention provides a method for directly preparing layer-number-controllable graphene on insulating substrates. The carbon-ion dosages are accurately controlled through ion injection, and different-layer-number graphene is directly prepared on the various insulating substrates. The method includes the steps that metallic nickel films are precipitated on the insulating substrates, then the carbon-ion dosages corresponding to the different layer numbers are injected into the nickel films through ion injection respectively, and thick copper films are precipitated on nickel; nickel and copper are mutually soluble at the high temperature, a large amount of copper can continually push carbon downwards, carbon is finally pushed out of nickel, and the graphene is formed at interfaces of the insulating substrates and nickel-copper alloy. By means of the method, the large-area-layer-number-controllable, high-quality and continuous graphene can be directly obtained on the different insulating substrates, further shifting is not required, and the quality of the graphene is greatly improved; high-temperature synthesis time is extremely short, the preparing efficiency can be greatly improved, and an effective and feasible way is provided for industrially preparing the high-quality graphene on insulators and applications of the graphene.