To improve oil recovery significantly, a novel polymer/surfactant binary system (SP) was formed by mixing a dendrimer-based polymer (noted HPMA) with sodium dodecyl benzenesulfonate (SDBS). A series of microcosmic strategies convincingly characterized that the dominating interaction of HPMA with SDBS was the electrostatic repulsion between the polymer branched chains and the head groups of SDBS. Meanwhile, a moderate hydrogen-bond effect and the solubilization of polymer branched chains could be observed respectively at stages of low and high SDBS concentration. Static experimental results indicated that these interactions would weaken the viscoelasticity of the SP system in comparison to that of the HPMA-only system, yet its interfacial activity could be reinforced. More significantly, sandpack tube displacement experiments directly demonstrated that the HPMA/SDBS composite system could effectively improve oil recovery through the synergistic effect of binary components. These results could provide theoretical guidance for the efficient use of the SP system according to actual demand.