Exploring ways to efficiently and inexpensively exploit and transport high-viscosity and high-pour-point crude oil is very important, and use of silica nanoparticles (nano-SiO2) to reduce the pour point and viscosity of this oil is promising. For this purpose, we modified nano-SiO2 in two ways. First, we used the coupling agent KH570 to replace hydroxyl groups in nano-SiO2 with organic groups. Next, we used four monomers (octadecyl methacrylate, styrene, maleic anhydride, and acrylamide) for graft copolymerization of the modified nano-SiO2 to obtain a nano-SiO2 composite. This method of modifying the nano-SiO2 surface reduces the agglomeration tendency of unmodified nano-SiO2 and disperses the composite material in the organic solvent. A synthetic nanocomposite material could reduce the viscosity of heavy oil with different viscosities and pour points by more than 60%. It could also reduce the pour points of heavy oil by more than 10 degrees C, thus showing superiority over the traditional ethylene-vinyl acetate flow modifier.