In order to evaluate the influence of supercritical CO₂ on the physical property of unconsolidated sandstone reservoir in Suizhong 36-1 oilfield, under the reservoir condition, the core porosity and permeability before and after gas injection were tested by using improved test device. The results showed that the porosity, gas permeability and liquid permeability of reservoir all decreased after contact reaction. The core porosity in average with 30% and 50% gas saturation decreased from 55.36% and 54.84% to 55.15% and 54.59%, the change rate was -0.4% and -0.5%, respectively. The core gas permeability of that decreased from 5.019 and 5.060 μm² to 4.925 and 4.952 μm², the change rate was -1.9% and -2.1%. The core liquid permeability of that decreased from 2.417 and 2.426 μm² to 2.289 and 2.291 μm², the change rate was -5.3% and -5.6%. Under the reservoir condition, corrosion products changed into the precipitation of carbonate because of the decrease of CO2 partial pressure. The larger initial porosity and permeability, the smaller decrease degree of reservoir physical properties was. Gas saturation had little effect on the change of reservoir physical properties.