In order to investigate the EOR mechanism of CO2 huff and puff for the single well in the carbonate fracturedcavity reservoir，a pressure-resistant physical model which contained three different well completion positions（upper position，middle positon and lower position）was designed and fabricated. The dynamic production performance of CO2 huff and puff in three completion positions with strong bottom water was studied firstly. And the effect of producing pressure drop，CO2 injection volume，and huff and puff cycles on CO2 huff and puff was researched. The xperimental results show that the middle completion position was the most suitable position for CO2 huff and puff，in which the recovery degree was 6.15% and the gas utilization factor was 0.887 mL/mL. CO2 injected from the middle positon could diffuse and dissolve in the heavy oil from two directions，which could expand the swept volume. Furthermore，there exists a suitable producing pressure drop during CO2 huff and puff. And the reasonable CO2 injection volume was then determined according to the producing pressure drop. Thus the highest recovery degree could be obtained. During the whole huff and puff，the ultimate recovery degree at the second cycle was the highest，and oil production of the previous four cycles of CO2 huff and puff accounted for 57% of the total oil production，which is the main oil production stage.