Experimental studies have been conducted to elucidate the fundamental mechanisms for the lowering of dynamic interfacial tensions (DIT) between crude oil and surfactant flooding systems with buffered alkaline. A series of novel single component alkylmethylnaphthalene sulfonates ( AMNS) including various carbon atom numbers of alkyl chains (hexyl, octyl, decyl, dodecyl, and tetradecyl), developed in our laboratory, were adopted. Moreover, surface tensions of various surfactant aqueous solutions were also investigated. It was found that AMNS surfactants exhibited great capability and efficiency of lowering the solution surface tension, and critical micelle concentrations were: 0.001-0.2 mass% and the surface tension at this concentration lambda(cmc) were 28.27-35.06 mN/m. It was also found that the octylmethylnaphthalene sulfonate (Oct-MNS), decylmethylnaphthalene sulfonate (Dec-MNS), and dodecylmethylnaphthalene sulfonate (Dodec-MNS) surfactants were greatly effective in reducing the interfacial tensions and can lower the tension of crude oil-water interface to ultra-low, even reaches 10(-6) mN.m(-1) at a very low surfactant concentration and optimum range of alkaline concentration. The DIT did not reach ultralow value when both hexylmethylnaphthalene sulfonate (Hex-MNS) and tetradecylmethylnaphthalene sulfonate (Tetradec-MNS) were adopted, respectively. To take both DITmin and DITeq into account, the Dodec-MNS surfactant exhibits excellent interfacial behaviors at a wide range of alkalinity from 0.2 to 0.8 mass% and surfactant concentration from 0.004 to 0.02 mass%. The added surfactants play an important role in reducing dynamic interfacial tension ( DIT) between oil and water. In order to lower DIT to ultralow, the optimal HLB values of surfactants ( from 7.1 to 9.0) were needed. The results exhibit that there exist both synergism and antagonism between the added surfactant and alkaline. The longer the alkyl chain length is, the less the needed alkalinity is.