The invention relates to a preparation method of a lithium niobate optical waveguide device, and belongs to the technical field of optical communication. According to the invention, a new cladding structure is introduced, a micron-order lithium niobate thin film optical waveguide device is obtained through the processes of ion implantation, BCB spin coating, bonding, annealing and the like, the preparation of a ridge waveguide is facilitated in process, the transmission loss of a finally prepared optical waveguide is effectively reduced, and the constraint of light is increased. According to the invention, a BCB is selected as a bonding medium material and used as an adhesive at normal temperature, so that a lithium niobate film and a substrate can be effectively combined together, the BCBis cured after annealing and used as a waveguide cladding, the subsequent mask etching process of a lithium niobate thin film is simple and convenient, and the lithium niobate thin film is not damaged; the optical refractive index of lithium niobate is 2.2, is greater than the refractive index 1.5 of the BCB and is greater than the refractive index 1 of air, and light can be well restrained in the waveguide, so that excellent performance can be realized without proton exchange.