The invention discloses a CO2 displacement experimental system and experimental method. The system comprises a gas refrigeration system, a gas injection system, a liquid injection system and a core clamping system. The gas refrigeration system is composed of a gas cylinder filled with CO2, a purifier, a refrigeration water bath, a first CO2 pump and a storage tank, wherein the gas cylinder filledwith CO2, the purifier, the refrigeration water bath, the first CO2 pump and the storage tank are sequentially connected. The gas injection system is sequentially connected with a second CO2 pump anda buffer tank through the storage tank. The liquid injection system comprises two branches connected in parallel. The first branch comprises a first piston container. The second branch comprises a second piston container. The inlet of the liquid injection system is sequentially connected with a liquid injection pump and a first container. The outlet is connected with the buffer tank. The core clamping system comprises a core holder. The core holder is connected with the gas injection system and the liquid injection system. The device provided by the invention can simulate and test the displacement process of carbon dioxide or an aqueous solution to the reservoir core under different displacements, different temperatures, different pressures and different solution ratios, and calculates residual water saturation or residual CO2 saturation.