The invention discloses a high-frequency copper foil substrate with an operating frequency of more than 1GHz, which has a dielectric constant Dk of less than 3.2 and a loss factor Df of less than 0.005 as well as high glass transition temperature, high thermostability and low moisture-absorption characteristic. The high-frequency copper foil substrate contains a special composite material and is prepared by impregnating a reinforcing material with blended resin mixture. The resin mixture of the composite material is prepared by blending the following materials: (a) high molecular weight polybutadiene resin; (b) low molecular weight polybutadiene resin; (c) modified polyphenyl ether thermosetting resin; (d) inorganic powder; (e) flame retardant; (f) cross-linking agent; (g) binding aid; and (h) hardening initiator. In the invention, the drawback of low processability of pure polybutadiene with low viscosity and the drawback of need of adding plasticizer of polyphenyl ether resin (PPE) with low solubility; particularly, the non-viscous pre-impregnated sheets made by the composite material can be processed into copper foil substrates automatically.