Because of the poor stability of ordinary foaming agents in high temperature reservoir environment，hydrophobic SiO2 nanoparticle was selected to enhance high temperature stability of benzene sulfonate foaming agent HY-4. Foam properties of HY-4 before and after compounding with nanoparticles were contrasted，while the foam stabilization mechanism of nanoparticles was discussed. Then，the temperature resistance of different foam systems were evaluated，as well as their high temperature plugging capabilities were compared. The results showed that the composite foam system with 0.5% HY-4 and 1.0% hydrophobic SiO2 nanoparticles had the best foam performance. The foam performance of composite system after aging 12 hrs was obviously better than that of HY-4 foam system below 150℃. The foam size of composite foam system was also smaller than that of HY-4 foam system，and it was little changed after 1 h standing. Besides，the core plugging capability of composite foam system was superior to that of HY-4 foam system at 150℃. And the foam of the composite system produced by the core had small particle size，high sphericity and strong compression resistance. Hydrophobic SiO2 nanoparticle could greatly enhance foam stability and improve foam plugging capability at high temperature