CO₂ flooding technology has the dual purpose of improving oil recovery and resource utilization and storage, and has been widely used in low permeability tight reservoirs. In order to clarify the influence of migration distance on gravity overlap degree caused by density difference during CO₂ miscible displacement, indoor physical model and numerical model were used to conduct research. The experimental results show that under the condition of miscible phase, the expansion space of gravity overlap is limited due to the decrease of core length, but the decrease of oil and gas miscible degree leads to a small reduction of gravity overlap degree; When the core length continues to decrease, the influence of the decrease of miscibility on the gravity overlap is greater than the influence of the core length on the space limitation of gravity overlap expansion, thus intensifying the gravity overlap. The numerical simulation results show that with the decrease of migration distance, the gravity overlap degree weakens and the miscible flooding recovery increases. Therefore, in combination with the field situation of the oilfield, in order to reduce the gravity overlap, the well spacing should be appropriately reduced to shorten the CO₂ gas migration distance, so as to improve the sweep efficiency of CO₂ flooding. The research results have certain guiding significance for the design of CO₂ flooding field test scheme and parameter optimization.