Emulsification tests and oil/water interfacial tension measurements were conducted to develop alkali/surfactant spontaneous emulsification system which was suitable to shengtuo high temperature and high salinity reservoir，and oil displacement efficiency of the spontaneous emulsification system were investigated by flooding test. The results showed that the interfacial tension of oil/water could be lowered to an ultralow level when adding 0.5 g/L of surfactant B4 to the 2 g/L NaOH+2 g/L Na2CO3 compound alkaline solution，leading to easy spontaneous emulsification of oil and forming emulsion under interfacial disturbance. Oil was emulsified by spontaneous emulsification system under the shearing action of porous media，the droplets might coalesce in the pore throat and generate strong jamin effect，and the mobility ratio of water to oil could be effectively reduced so as to increase the sweep efficiency and oil recovery. Droplets were ether entrained along with flowing aqueous phase to improve oil displacement efficiency. While emulsification and entrainment still leaded to the oil recovery enhance and pressure drop，it did not seem to be as effective as emulsification and entrapment. The optimal spontaneous emulsification formula was as follows: 2 g/L B4+2 g/L NaOH+2 g/L Na₂CO₃，and the oil recovery increased by 21.5% by spontaneous emulsification flooding and the oil recovery did not decrease with the increase of the sandpack length.