The acidic fluid formed by CO2 dissolved in water could dissolve sandstone in the process of CO2 flooding in reservoirs. The dissolution could change the physical properties of the reservoirs and obviously affect the oil recovery. Therefore，the static immersion experiment and dynamic displacement experiment of CO2 flooding in sandstone reservoirs were carried out to quantitatively study the influence of dissolution on the physical properties of the reservoirs under different temperature and pressure conditions. The experimental results show that the dissolution effect is obvious in the process of CO2 immersion and flooding. The porosity and permeability increase with the increase of temperature and pressure exponentially. The mathematical expression equations of the relationships between the temperature，pressure and porosity change rate and permeability change rate were obtained based on the experimental data. The numerical simulation study was carried out on Block H3 of Changqing Oilfield with the aid of mathematical equations. The results showed that the dissolution in the overall reservoir of the study area occurred，and the dissolution degree in the injection well area was higher. The oil recovery considering dissolution is 26.08%，but the oil recovery without considering dissolution is 21.03%. The enhanced oil recovery（EOR）is 5.05%.