In response to the limitation of chemical flooding systems based on surfactants and polymers in enhancing oil recovery in high-temperature (>100°C) and high-salinity (22.5×104^mg/L) streamway sand reservoirs, it is proposed to modify nanomaterials to simultaneously improve water flooding sweeping efficiency and micro oil washing efficiency. Firstly, the chemical modification of nano-SiO2 is carried out to empower and characterize its structure. Then the ability of modified nano-SiO2 to form viscosity increasing emulsion with crude oil, the ability to reduce interfacial tension and the feasibility of enhancing oil recovery under heterogeneous conditions are studied. The experimental results show that the modified nano-SiO2 has a surface branching number of 105. The modified nano-SiO2 can form viscosity increasing W/O emulsion with crude oil in the range of 10%~80% water content, and the viscosity of emulsion is 2~10 times of the viscosity of crude oil. Modified nano-SiO2 can reduce the interfacial tension between oil and water to 10-3^{mN/m. Modified nano-SiO}2 in porous media improves macroscopic sweep efficiency through flow control and Jamin effect, and enhances microscopic oil washing efficiency by reducing interfacial tension. After water flooding to a water content of 98%, modified nano-SiO2 flooding and subsequent water flooding can increase oil recovery by more than 25%. All experimental results indicate that increasing viscosity of nano-SiO2 is feasible for improving oil recovery in river sand reservoirs.