Nanoparticles can improve the stability of CO2 foam and increase oil recovery during CO2 flooding in reservoirs. However, there are few reports in the literature concerning the synergistic effects of hydrophilic nanoparticles and nonionic surfactants on the stabilization of CO2 foam. In this study, the mechanism of the synergistic stabilization of CO2 foam by the nonionic surfactant C12E23 and hydrophilic T40 nanoparticles (SiO2) and the flow characteristic in porous media were investigated. Furthermore, the best formula for CO2 foam has been determined. The experimental results show that the nonionic surfactant C12E23 adsorbs on the surface of T40 nanoparticles by van der Waals forces and hydrogen bonds, which increases the hydrophobicity of the nanoparticles. In the dispersion of 2.49 mM C12E23 and 1.5 wt % T40, the surfactant forms a dense monolayer on the surface of nanoparticles, and the hydrophobicity of the nanoparticles reaches the maximum with a contact angle of 78. The stability of the CO2 foam under this condition is the best with an initial foam volume of 280 mL and a half-life of 150 min. The half-life is 30 times greater than that of the C12E23 foam. The nonionic surfactant C12E23 and hydrophilic T40 nanoparticles synergistically stabilize the CO2 foam by three aspects. First, the adsorption of nanoparticles at the gas liquid interface reduces the interfacial tension. Second, the nanoparticles increase the interfacial viscoelastic modulus, which considerably improves the mechanical strength of the foam film. Third, the nanoparticles increase the viscosity of the dispersion, which increases the liquid holdup of the CO2 foam. The C12E23/T40 foam can also increase the sweep area and displacement efficiency and thus enhance oil recovery during flooding in porous media. The results are of strong significance to improving the recovery efficiency of CO2 foam flooding.