Winsor Ⅲ microemulsion flooding is an effective means to solve the low production percentage of high-temperature，high-salinity and low-permeability reservoirs，but the research on the construction and mechanism understanding of Winsor Ⅲ microemulsion flooding system is insufficient. In this paper，the Winsor Ⅲ microemulsion system with temperature resistance and salt resistance was constructed through the solubility test，oil-water interfacial tension test，and phase behavior test of two types of surfactants and their composite systems under the conditions of simulated reservoirs. Then，the feasibility of the system in enhancing oil recovery of low-permeability reservoirs was explored through core displacement experiments，contact angle testing experiments，and visual core displacement experiments. The mechanisms of enhancing oil recovery were analyzed from two aspects：changes in wettability and solubilization and emulsification. The results show that alcohol ether carboxylate surfactant ST 982-B can construct a Winsor Ⅲ microemulsion system at the mass fraction of 0.3%-0.5%；the microemulsion system can effectively enhance oil recovery of low-permeability reservoirs by 7.8%-9.7%. The microemulsion system can effectively improve the rock wettability，and the“denudation”of oil film after solubilization and emulsification of the system further enhances the oil displacement efficiency.