This study proposes a co-linear scheme for generating strong terahertz radiation in a lithium niobate source using a contact grating method. This scheme achieves co-linearity between the incidence direction of pump light and the radiation direction of terahertz wave, thereby directly eliminating the complex angle adjustment required in traditional tilted-pulse-front technologies. Moreover, the scheme has a compact structure, simple optical path, and high radiation efficiency, laying a strong foundation for the widespread application of lithium niobate terahertz sources. We analyze the design of the contact-grating structure and the nonlinear interactions within the lithium niobate crystal using structural simulation, theoretical derivation, and numerical simulation. Further, we derived optimized grating structure parameters and obtained the radiation field intensity distribution of terahertz waves propagating inside the lithium niobate crystal. The simulation results show that the terahertz radiation energy reaches its maximum value after the pump light propagates a certain distance. This simulation obtained the position of the maximum value and determined the optimal thickness of the crystal, providing a reference for the production of lithium niobate strong terahertz radiation sources.