Regular and hydrophobic petroleum sulfonates were extracted and purified from the crude samples of petroleum sulfonates used in shengli oilfield by liquid-liquid extraction method. Analysis of these substances using liquid chromatography, mass spectrometry and determination of hydrophile-lipophile balance values were completed. Meanwhile, interfacial tension values of oil/water system respectively consisted of regular and hydrophobic sulfonates were measured by rotated dropping method. The results show that hydrophobic sulfoantes are different from regular sulfonates in composition, and it mainly consists of mono sulfonates, while the contents of mono and disulfoantes in regular sulfonates are similar. Meanwhile its interfacial activity is much lower than that of regular sulfonates, and it can not obtain ultralow interfacial tension values, not only for unit but also for mixed systems. While mixed systems of regular sulfoantes can decrease interfacial tension values to 10^-4 mN/m. Besides, the relationship between the structure of petroleum sulfonates and their interfacial activities was discussed.