The fracture-matrix model was designed by improving traditional oil displacement experimental device to simulate fractured reservoirs. Miscible continuous CO2 injection and CO2 huff-n-puff process were carried out in fracture-matrix system to investigate the EOR characteristics of miscible CO2 injection. The composition of produced oil during CO2 injection was tested to analyze the main mechanism of oil production at different continuous gas injection times. The results indicate that the miscible continuous CO2 injection cannot significantly increase oil recovery of the fracture-matrix model.The oil recovery factor was only 18.2% when the length of matrix was 10.0 cm，and decreased to 14.1% when the length of matrix was 20.0 cm. The compositional tests of crude oil show that after 0-8 h of CO2 injection，the content of produced oil was similar to that of the initial crude oil. Oil swelling were the major production mechanism contributing to the oil recovery during this period. The most of the produced oil during continuous CO2 injection was produced by oil swelling. After 8-40 h of CO2 injection，the content of produced oil changed obviously because the hydrocarbon extraction is the main oil production mechanism. However，the incremental oil content is little during this period. The oil recovery during the CO2 huff-npuff process may be significantly enhanced by 72.8% to 73.9% after continuous CO2 injection. But the oil recovery is strongly influenced by differential production pressure. When the production pressure difference was 5 MPa，the oil recovery factor varied between 7.9% and 12.4%. When the production pressure difference was increased to 20 MPa，it was up to 73.9%.