Carbonized intelligent water flooding is a new chemical combined oil recovery method. How to improve the solubility of CO₂ in salt water is the key to effectively reduce the interfacial tension between oil and water. The formation water with high salinity was diluted as smart water，and CO₂ was added to the smart water with different concentrations of mutual solvent under different pressures. The interfacial tension measurement experiment was carried out to study the influence of mutual solvent on the interfacial tension between smart water（or carbonized smart water）and crude oil，and the influence of salinity，mutual solvent concentration and pressure on the interfacial tension of oil and water was clarified. The experimental results showed that the density of the mixed liquid and carbonized smart water decreased with the increase of the concentration of organic mutual solvent，and with the increase of the system pressure，the density of the mixed liquid slightly increased，while the density of the carbonized smart water decreased. Under constant pressure，the interfacial tension between the mixed liquid and crude oil decreased with the increase of the mutual solvent concentration in the mixed liquid，and decreased with the decrease of the salinity，but it was less affected by the system pressure. The decrease of the interfacial tension of the mixed liquid under the action of DME was greater than that under the action of methanol. When CO₂ was added to smart water，the interfacial tension of oil and water could be further reduced. The interfacial tension between carbonized smart water and crude oil decreased with the increase of mutual solvent concentration，and decreased with the decrease of salinity and system pressure. The interfacial tension between the carbonized smart water and crude oil was the smallest when 10% formation water was added with 15% DME and then 9 MPa CO₂ was added，and the interfacial tension was reduced by 88.2%. The research results provide a new method for the continuous development of old oil fields with high water cut and the improvement of water flooding recovery.