Abstract: How to effectively improve the recovery factor has always been a difficulty for extra-low permeability reservoir development. Taking the Triassic Chang-6 reservoir, a typical extra-low permeability reservoir in Changqing oilfiled as a case, the paper studies the oil displacement systems which could match with the reservoir characteristics to improve the oil recovery factor. Based on the evaluation of the oil displacement efficiencies of different displacement systems with different interfacial activities, emulsifying properties and viscosities, the paper identifies that the emulsifying property is the primary indicator of the screening of surfactant for extra-low permeability reservoirs, followed by the interfacial activity. When the oil displacement agent has the both characteristics, the oil displacement efficiency can be greatly improved. A surfactant flooding system with high interfacial activity, strong emulsibility and low viscosity is screened out and the result of core displacement experiment shows that the CQ-I system can increase oil displacement efficiency by more than 28.9% based on waterflooding. Based on the results of indoor research, a field test of 4 well groups was carried out in District A of W Oilfield in Changqing oilfield. By the end of December 2017, the incremental oil production of the test well group was 5 889.9 t, and the input-output ratio was 1∶2.25 at that stage, showing good application effects