The invention discloses a silicon-based lithium niobate high-speed light modulator and a preparation method thereof. The modulator comprises a silicon substrate wafer, a lower silicon dioxide cladding, lithium niobate film, an optical waveguide, a metal electrode, a silicon V-shaped groove and a coupling optical fiber, wherein the lower silicon dioxide cladding is located on the upper surface of the silicon substrate wafer, and the lithium niobate film is located on the lower silicon dioxide cladding. The silicon-based lithium niobate high-speed light modulator has the advantages that heterogeneous integration of a lithium niobate single crystal body and a silicon single crystal body is achieved; by utilizing the thin-film lithium niobate wafer and the characteristics such as low dielectric constant and low dielectric loss of the lower silicon dioxide cladding, improvement of modulation rate (or modulation bandwidth) of the lithium niobate light modulator can be achieved; by utilizingthe thin-film lithium niobate wafer and the high insulativity of the lower silicon dioxide cladding, intensity increase of microwave electromagnetic fields distributed in the lithium niobate film canbe achieved, the modulation efficiency of electric fields to light fields is improved, and the driving voltage of the modulator is reduced.