Aiming at the problems of large size, high insertion loss, and complex process of multi-mode interference （MMI） coupler, a 4×4 MMI coupler based on transverse electric （TE） mode is designed on the platform of X-cut thin-film lithium niobate（X-cut TFLN）. The length and width of the MMI region are simulated and optimized using the three-dimensional finite-difference time-domain （FDTD） method. Finally, a 4×4 MMI coupler is manufactured on the platform using inductive coupled plasma（ICP） etching method according to the optimization results. The simulation results show that the total insertion loss of the optimized 4×4 MMI coupler is 0.36 dB, and the actual measured insertion loss is 0.78 dB.