For the characteristics of water injection pressure rising fast and difficultly injecting in the water injecting process in Chao Yanggou low permeability oilfield, the lowering pressure and increasing injecting surfactant system was screened and the recipe of surfactant system was determined as follows:0.2% Petroleum sulfonate salts surfactant T702-40# surfactant+ 0.5% Na₂CO₃. The experimental results indicated that the equilibrium interfacial tension between the surfactant system and the Chao Yanggou crude oil could reach 2×10^-2 mN/m, the of the surfactant system had good temperature resistance and salinity resistance, and had good compatibility with injecting water and formation water, and could make the rocky wettability reverse, which make the oil recovery be improved by about 5%. The movable permeability value calculated from the surfactant system flooding was 15% bigger than that of water flooding, which could reduce start-up pressure obviously. And the mechanism of surfactant system reducing start-up pressure was researched. Field test results of 82-152 well area in Chao Yanggou oilfield indicated that the surfactant system could reduce start-up pressure, improve reservoir water absorbing capacity, increase producing proportion of low permeability reservoir, and cumulative oil increment of 7 wells was 1768 t.