Emulsification and viscosity reduction is one of the key techniques for enhancing the recovery efficiency of heavy oil. Due to the inability of conventional viscosity reducers to meet the high temperature and high salinity requirements during thermal recovery of highly viscous oil, issues such as viscosity reducer deactivation, poor viscosity reduction performance, and low recovery rates often arise. This study focuses on the preparation of a nano viscosity-reducing oil displacement system through laboratory experiments, characterizing the microstructure of the nano materials. The study evaluates the viscosity reduction effect on highly viscous oil, as well as the system"s temperature resistance, salt resistance, rock spreading effect, adsorption loss, and oil displacement efficiency.The composition of the system formula is as follows: 50% SiO2 + 40% dispersant EB-1 + 4.2% surfactant 2 + 5.8% synergist ZX. Experimental results indicate that the 1% concentration nano viscosity-reducing oil displacement system achieves a viscosity reduction effect of 84.99% on highly viscous oil. After aging for 2 hours at a temperature of 350°C and a salinity of 15000 mg/L, the viscosity reduction performance retention rate remains at 99.27%. The system causes a wetting reversal on the reservoir rock surface. At a liquid-solid ratio of 10:1, the static adsorption capacity of the system is 1.328 mg/g of sand, and the dynamic adsorption capacity is 0.745 mg/g of sand, both lower than the standard adsorption capacity of 2 mg, resulting in low adsorption losses in the reservoir. Through one-dimensional displacement experiments, the system exhibits a 26.7% improvement in oil displacement efficiency compared to conventional steam flooding.The study of the nano viscosity-reducing oil displacement system can effectively enhance the thermal recovery efficiency of highly viscous oil.