The minimum miscibility pressure（MMP）of the CO2-crude oil system is a key factor affecting the development effect of CO2 flooding. When the reservoir pressure is lower than the original saturation pressure，the part solution gas dissolved in the oil will be separated from the oil with the development of oil reservoir. Thus，the composition of oil phase and its high-pressure physical properties will also change，which will affect the MMP of CO2-crude oil system. The MMP obtained from the original formation oil sample is no longer applicable. Based on the slim tube experiment and multi-component numerical simulation，the MMPs of crude oil samples at different reservoir pressures in eight typical blocks of an oilfield in western China are systematically studied. Compared with other oilfields in China，the C1 molar content of oil samples from various reservoirs in the study area is higher，ranging from 31.12% to 51.69%，with an average of 43.25%；while the molar content of C2-C6 is lower，ranging from 8.0% to 18.48%，with an average of only 11.3%. The experimental and simulation results show that CO2 can be miscible with the oil samples from eight typical blocks under at original reservoir pressures，but the MMPs of CO2 flooding in various blocks have significant differences，ranging from 17.60 MPa to 41.18 MPa. After the reservoir pressure is lower than the original saturation pressure，the MMPs in CO2 flooding of typical reservoir oil samples tend to decrease slightly. With further decrease of degassed pressure，the molar content of C1N2 in the oil phase decreases，the molar contents of C7+and C24+ increase，and the changes of C2 and C3+ are minor. C1 is the main component of the separated gas at different pressures. The intermediate component increases sharply only at the last degassing pressure. CO2-crude oil miscible zone occurs at the swept front of the injected CO2 close to the injection side. The miscible zone becomes wider with the displacement.