The invention belongs to the technical field of production of magnetic oxide films, and particularly relates to a preparation method for directly growing a highly-doped yttrium iron garnet film on silicon. The laser energy density in the growth process of a rare earth-doped yttrium iron garnet film is changed from 1.8 J/cm<2> to 4.0 J/cm<2>, the film deposition temperature is changed from 400 DEG C to 850 DEG C, and the film deposition air pressure is changed from 1 mTorr to 20 mTorr, so that the rare earth doping concentration in the yttrium iron garnet film growing on a silicon substrate is improved from 33% to 50%, the Faraday optical constant of the material in photo-communication 1550 nm wavelengths is improved from 2800 degrees/cm to 6000 degrees/cm, and the magneto-optical property of the material is greatly enhanced.