Abstract: Tight oil reservoirs, as an important part of unconventional oil and gas resources, their efficient development is of great significance for ensuring energy security. However, constrained by reservoir characteristics such as low porosity, low permeability, and strong heterogeneity, the application effect of traditional development methods in tight oil reservoirs is poor. At present, due to its unique physical and chemical properties, CO₂, as a key injection medium, is widely used in the development of tight oil reservoirs, and CO₂ displacement technology is gradually becoming one of the core means to break through the bottleneck of recovery efficiency of unconventional oil and gas resources. Based on the multiphase, multicomponent, and multiple-relaxation-time lattice Boltzmann method (LBM), this work couples the Shan-Chen pseudopotential multiphase flow model with displacement boundary conditions to propose an improved multiphase flow displacement LBM. Using this method, comparative validations are conducted for interfacial tension, contact angle, and the diffusion process of CO₂ in the oil phase. The Péclet number is introduced to establish quantitative characterization relationships among the diffusion coefficient, Péclet number, and CO₂-oil interaction parameters. Furthermore, numerical simulations analyze key parameters in the CO₂ displacement process and quantitatively evaluate the displacement efficiency under the influence of different key parameters. The results show that for CO₂ immiscible displacement, the combined effect of capillary number and viscosity ratio significantly influences the displacement efficiency after CO₂ breakthrough, and different wettabilities affect the immiscible displacement effect and the distribution pattern of remaining oil. For CO₂ miscible displacement, the displacement efficiency and oil recovery rate are the lowest at a low Péclet number; a high Péclet number enhances displacement instability, leading to a gradual decrease in displacement efficiency. When the Péclet number is around the unity, the synergistic coupling effect of molecular diffusion and viscous flow is maximized, maintaining a high displacement efficiency. The influence mechanism of the Péclet number has certain viscosity dependency: for different viscosity ratios, a lower Péclet number can effectively suppress the viscous fingering caused by them. Compared with CO₂ immiscible displacement, miscible displacement can effectively enhance oil recovery in the actual development of tight oil reservoirs due to lower interfacial tension and oil viscosity.