Abstract: Two strains of bacteria with good oil displacement effect as a bio?surfactant were isolated from Ansai low?permeability reservoir,which were identified as Pseudomonas aeruginosa DN001 and Bacillus subtilis DN002. The ability of reducing the surface tension and interfacial tension, emulsion performance of crude oil and environmental adaptability for the two microbes were evaluated in experiment. The results show that the fermented liquid of the combination bacteria strains can reduce the surface tension of water from 72 to 25.1 mN/m and has high oil?water interfacial activity with the equilibrium interfacial tension of 0.954 3 mN/m. The screened microbial bacteria can thrive in Ansai reservoir environment. The core displacement experiment indicates that microbial combination flooding can improve recovery by 17.38%. These results show that the screened strains have a good performance in enhance oil recovery and provide a reliable experimental basis for the field application in Ansai reservoir