CO₂ flooding that is a kind of developed EOR technology with widely prospect of application, becomes the focus of attention in many countries. In the CO₂ flooding, rock can react with CO₂ dissolved in the water, which changes the pore structure and wettability of rock, and so on. In order to determine the change rule on pore structure and wettability of rock treatment of CO₂ flooding, in this paper under the actual condition of daqing F reservoir, using the simulation of the actual reservoir conditions, the changes of rock properties for natural core treated by CO₂ flooding are studied by the experimental methods of indoor research. The results show that as CO₂ injected the rock is changed on pore structure, permeability and wettability, and so on. As the contact time of rock reacted with CO₂ increases, the percentage of small pore and big pore increases, but the proportion of secondary porosity decreases, meanwhile the permeability and the hydrophilicity gradually increase. This result is caused by the release of CO₂ that can lead to the acidifying effectreacting with the mineral composition on the pore surface of rock, and then change the rock pore structure and the mineral composition of the rock surface.