A C-SiO2/polyacrylamide (PAM)/ polyethylenimine (PEI) gel system was constructed using cetyltrimethylammonium bromide modified SiO2 (C-SiO2) as reinforcing agent, and its temperature resistance, salt resistance and long-term stability were investigated in simulated reservoir environment. The results showed that C-SiO2/PAM/PEI could not form gel under acidic environment, while its gelation time decreased and gel strength increased at pH≥7. The gelation time reduced from 20 h to 1 h and the gel strength reached to grade I with the rising temperature from 30 ℃ to 120 ℃. In addition, The gelation time of C-SiO2/PAM/PEI was postponed from 3 h to 5 d and the gel strength reduced from grade I to G when the salinity of NaCl solution increased from 0 mg/L to 100000 mg/L. Under the condition of 120 ℃, pH = 9, NaCl solution with salinity of 70,000 mg/L, C-SiO2/PAM/PEI gel system had ultimate strength of grade H, apparent viscosity of 600000 mPa·s, and maintain more than 360 d without dehydration, with good long-term stability. The results showed that C-SiO2 and PAM molecules could form hydrogen bonds, which forms more compact 3D network structure, thus improved the water-holding capacity of C-SiO2/PAM/PEI. In addition, the strength of C-SiO2 improved the strength, temperature resistance and long-term stability of the gel system.