CO₂ oil displacement technology plays a key role in carbon emission reduction and enhanced oil and gas recovery. This study focuses on the numerical simulation of CO2 oil displacement, and establishes a one-dimensional three-phase mathematical model under column coordinates. The simulation results show that in the immiscible displacement process, the formation pressure increases gradually, and the pressure difference between borehole and formation shrinks continuously. The rise rate of water phase saturation slows down. Oil phase saturation rose first and then decreased, and the annular effect of displacement was significant. CO2 gas phase saturation increased until it occupied the remaining pore space, and its change rate gradually decreased. This study reveals the spatial distribution of reservoir physical properties in the process of CO2 flooding, explains the oil flooding mechanism and influencing factors, and is of great significance to enhance oil recovery.