In order to reduce the interfacial tension between oil and water in alkali-free binary flooding and maintain the viscosity of polymer solution at the same time，aiming at the formation conditions of Shengli ST oilfield，the effects of surfactants such as oleic acid amide carboxybetaine（OAB）and alkanolamide（WCXA）on the viscosity of hydrophobic associating polymer（AP）solution and its interfacial tension with crude oil of Shengli ST oilfield were studied. And the oil displacement performance of binary oil displacement system composed of compound surfactant and AP was evaluated. The results showed that the interfacial tension between the binary system composed of single WCXA or OAB and polymer AP and crude oil could not reach ultra-low value. The combination of WCXA and OAB could produce synergistic effect. Increasing the proportion of WCXA could improve the retention rate of viscosity，while increasing the proportion of OAB was beneficial to decrease the interfacial tension between oil and water. When WCXA and OAB were compounded in a mass ratio of 3∶1，the dosage of compound surfactant was 0.1%-0.4%，and the dosage of AP was 0.15%—0.25%，the interfacial tension between oil and water could be reduced to 10^-3 mN/m order of magnitude in 2 hrs，and the viscosity retention rate of polymer ranged from 102% to 111%. The composite system of 0.25% AP and 0.4% composite surfactant could improve oil recovery by 36% on the basis of water flooding，showing good oil displacement effect.