Abstract: In order to study the improvement of oil displacement efficiency by superheated steam injection, an indoor single-tube experiment was carried out to study how the steam quality and injection rate influence the recovery factor, and the oil displacement mechanism was analyzed from four aspects：viscosity, permeability, thermal expansion coefficient and distillation ratio. The results show that when the steam injection rate is 1.8 mL/min, the steam with 15 ℃ degree of superheat is the optimal injected steam quality and the ultimate recovery factor can reach 77.8%; when the optimal steam quality is injected, the optimal steam injection rate will be 1.3 mL/min, and the ultimate recovery factor can reach 79.6%. After the oil displacement by superheated steam, the viscosity of heavy oil at 50 ℃ can be reduced by 40.7%. The average thermal expansion coefficient of the experimental oil is 0.000 653 ℃-1, the oil temperature increases by 300 ℃ and its volume will increase by 19.6%. The superheated steam will cause the transformation of montmorillonite and kaolinite to chlorite or illite, physical washing can increase the pore channel and improve the reservoir seepage behavior