To investigate the flooding performance of SiO2 nanofluid in low permeability reservoirs，the self-developed modified hydrophobic nanosilica was used to study the stability of SiO2 nanofluid and its effect on interfacial tension. Series of flooding experiments in low permeability cores were conducted to evaluate the performance of SiO2 nanofluid and to optimize the injection parameters. The results showed that the average size of SiO2 nanoparticles was about 50 nm；when the particle concentration was 0.15%，the interfacial tension value was the lowest，being of 0.55 mN/m；when the concentration was below 0.15%，the stability of the system was good，and the higher the concentration，the worse the stability of the system. Flooding experiments in cores with 20×10-3 μm2 showed that SiO2 nanofluid could effectively reduce water cut and injection pressure. The injection parameters reached its optimization when the injection rate，injection volume and particle concentration was 0.1 mL/min，0.5 PV and 0.15% ， respectively. Under these conditions，oil recovery could be enhanced by 25.41%. The SiO2 nanoparticles with hydrophobicity synthesized in this study can be used to efficiently enhance oil recovery in low permeability reservoirs.