In order to study the microscopic migration characteristics of heavy oil by CO2 flooding and its influence on the recovery at high temperature and high pressure（70 ℃，8 MPa），the microscopic visualization simulation system of high temperature and high pressure was used to simulate the displacement process of heavy oil by CO2 flooding in different stages and different regions，and its microscopic migration characteristics were studied. The effect of CO2 on recovery of heavy oil in this process was quantitatively analyzed. The results show that the process of CO2 flooding can be divided into three parts：oil and gas being soluble with each other，asphaltene precipitation，and gas-carrying asphaltene particles migration. At the stage of first gas flooding，CO2 moves freely with small bubbles，and then deformation，merge or splitting occurs. Finally，dominated by continuous phase migration. During the closing time，CO2 dissolves in heavy oil and precipitates out with asphaltene；at the stage of second gas flooding，CO2 carries some asphaltene particles and migrates continuously，and the swept volume increase. In addition，the reaction conditions in the process of CO2 flooding are adjusted to balance the interaction of gas viscosity reduction and asphaltene precipitation，so as to promote the effective migration of oil and gas and improve the recovery.