For understanding effects of molecular structure on properties of surfactants an asymmetric double long-chain alkyl betaine, stearylhexylmethyl carboxyl betaine (C18+6B), was synthesized using stearic acid and hexanoic acid as starting materials and its surface active properties were measured and compared with that of didodecyl methyl carboxyl betaine(diC12B), a symmetric double long-chain betaine with equal total carbon number. The results show that C18+6B has a surface activity similar to that of diC12B in general, but displays an aqueous solubility much better than that of diC12B. As a surfactant for surfactant-polymer flooding free of alkali, C18+6B seems to be slightly less hydrophobic against Daqing crude oil, which solely can reduce the Daqing crude oil/connate water interfacial tension (IFT) to 10-2 mN/ m magnitude and gives a saturated adsorption 30% lower than that of diC12B at Daqing sandstone/water interface at 45 C. C18+6B solely can reduce C7-C9 n-alkanes/connate water IFT to 10-3 mN/m magnitude at 45 C, and can reduce the daqing crude oil/connate water IFT to 10-3 mN/m magnitude at 45 C by mixing with the more hydrophobic surfactant diC12B and other hydrophilic betaine surfactant, where the aqueous solubility of the formulation is greatly improved by the presence of C18+6B.