Large-scale integration of traditional optical waveguide and electronic crystal devices cannot be realized because of optical diffraction. However, this restriction has been lifted by surface plasmon technology by providing the possibility of restraining and manipulating the light energy at the nano scale. In this study, the surface plasmon waveguide device of glass–lithium niobate–gold–lithium niobate has been designed. The structure consists of four layers: the first layer is glass, the third layer is periodic grating, and next to the grating is a symmetrical structure of lithium niobate. The grating thickness, LiNbO3 thickness, and Au grating width are used for modal analysis of the waveguide structure. Then, the test range of each parameter is adjusted in accordance with the simulation results to determine the optimal geometric parameters. Results show that the transmission loss is as low as 0.0004–0.0017 cm−1 and the normalized mode area is always less than 0.053 when the thickness range of lithium niobate is from 380 to 400 nm. Meanwhile, the optimum geometric parameters of the structure are obtained using comprehensive analysis of the simulation. The normalized field area is 0.0334 and the propagation loss is 0.0004 cm−1 when the Au thickness is 150 nm, the LiNbO3 thickness is 389 nm, and the grating width is 42 nm. In this condition, the waveguide can obtain deep subwavelength mode limiting capacity while reaching the minimum propagation. The structure can fully achieve the deep subwavelength constraints for the light field and exhibits excellent waveguide characteristics.