Abstract: Nanometer-silicon dioxide was prepared with sol-gel method and modified by organic modifier.The nanometer-silicon(dioxide)and the modified nanometer-silicon dioxide were respectively composed with petroleum sulfonate which is widely used in oilfield.The ability of the composite system for reducing the oil-water interfacial tension was measured by interfacial tensiometer TX-500.The result showed that petroleum sulfonate,and nanometer-silicon dioxide and petroleum sulfonate composite system could(reduce)the oil-water interfacial tension to about 0.01 mN/m,and modified nanometer-silicon dioxide and petroleum sulfonate composite(system)could reduce that to about 3.37×10^-3 mN/m,when the concentration of surfactant was 1%.The modified nanometer-silicon dioxide added into petroleum sulfonate could reduce the oil-water interfacial tension,which was favorable to enhanle oil recovery.