Polymer flooding is an important method for enhancing oil recovery during oilfield development. However, the performance of polymers is limited by temperature and salinity, which affects their oil displacement efficiency in reservoirs. Recent studies have found that a mixed solution of polymers and nanoparticles can enhance the rheological properties of polymers and improve their oil displacement efficiency, especially in harsh geological environments where this effect is more pronounced. This experiment aims to investigate the rheological properties of polymer-nanoparticle composite solutions and their impact on reservoir recovery. Using a high-temperature and high-pressure rheometer, the rheological properties of polymer and nanoparticle composite solutions were analyzed. Additionally, a microfluidic device was used to study the oil displacement mechanism of these composite solutions. The results indicate that adding a high concentration of nanosilica to the polymer solution significantly improves its temperature and shear resistance. Experiments have found that when the temperature exceeds a certain critical point, viscosity increases with rising temperature. Furthermore, the oil displacement efficiency of the HPAM/NPs composite system is superior to that of nanosilica solution or water flooding alone.