After depleted production of high-pressure and low-permeability reservoirs，the formation energy is insufficient，which leads to the increase of gas production because of oil degassing. Therefore it is feasible to reinject the produced gas from economical and technical aspects. In order to clarify the microscopic oil displacement mechanism of reinjected natural gas flooding after the depleted production of this kind of reservoir，the factors influencing natural gas flooding is analyzed under high-temperature and high-pressure conditions so as to reveal the influence of depleted production and water flooding on natural gas flooding effect. Using self-developed high-temperature and high-pressure micro-visualization device，the microscopic gas displacement experiments under various conditions are carried out on the glass-etched porous medium simulation model. The results indicate that natural gas flooding can reduce the Jamin effect caused by degassing of oil during depleted production.Under the target reservoir conditions，the gas flooding mechanism is dominated by displacement，and the dissolution extraction is supplemented. Water barrier prevents the contact between gas and oil.In unswept area of natural gas，the residual oil is difficult to be produced because of water barrier，in swept area，natural gas can peel off water film gradually to contact with oil，and displace oil by dissolution and extraction. Natural gas flooding in high-pressure and low-permeability reservoirs can further enhance oil recovery after depleted production.