In order to obtain a internal olefin sulfonate（IOS）microemulsion system with good oil displacement performance，the optimum formula of C24-28IOS/t-pentol/Na2CO3/NaCl microemulsion was determined by orthogonal test，then the displacement mechanism of the IOS microemulsion system to five kinds of remaining oil was studied through microscopic oil displacement test， and the oil displacement effect of the system was analyzed by oil displacement experiment of low permeability core. The performance of microemulsion system was evaluated，and it was applied in Daqing oilfield. The results showed that the IOS microemulsion with 0.3% C24-28IOS，0.6% t-amyl alcohol，1.25% NaCl and 1.25% Na2CO3 was close to the mesophase state. Microemulsion could form low interfacial tension with oil，reduce residual oil saturation and improve oil recovery. Microemulsion had the function of emulsification and viscosity increasing，which could control the fluidity and expand the swept volume in the process of displacement. Meanwhile，due to the elasticity of microemulsion，its deformation micro force played an important role in improving oil displacement efficiency. The results of core flooding experiment showed that IOS microemulsion had obvious effect of increasing oil and decreasing water cut. Compared with water flooding，microemulsion had 9.16% higher displacementefficiency and 8.2% lower water cut. The injection of IOS microemulsion in the later stage of high water cut development in lowpermeability reservoir could obviously increase oil production.