This study proposes a large bandwidth two-dimensional grating coupler based on the lithium niobate platform. By introducing a lithium niobate crystal comprising a photoelectric material as the platform, a silicon triangle structure is adopted, and based on the effective medium theory, the transverse width of each triangle is changed along the direction of light propagation. A low refractive index oxide buffer layer is introduced between the silicon grating coupler and the bottom of lithium niobate thin film (LNTF) waveguide. A vertical grating coupler with a coupling efficiency of 60.8% and a 1 dB bandwidth of 102 nm is obtained at a wavelength of 1550 nm.