The oil reservoirs in the western South China Sea have entered a high water cut stage with significant reservoir heterogeneity. High-temperature profile control is urgently needed for injection wells to improve oil recovery. Aiming at the high temperature（130 ℃），high salt（32 385 mg/L salinity，5650 mg/L calcium and magnesium ion content）environment of the oil reservoir in the western South China Sea and the failure of conventional organic gel channeling sealing system，a nano-silica toughened gel with temperature resistance and salt resistance was prepared by using acrylamide and 2-acrylamide-2-methylpropane sulfonate sodium copolymer（GW-1），resorcinol，urotropine，acetic acid and amine modified nano-silica toughened agent（20 nm） as raw materials，and then the gel formula was optimized. The gelation kinetics equation of gel at 90—130 ℃ was obtained by the relationship curve between gelation time and crosslinking agent dosage. Finally，the viscoelasticity，injectivity and plugging ability of nano-silica toughened gel were evaluated and compared with those of none-toughened phenolic gel. The results showed that the optimum formula of nano-silica toughened phenolic gel was obtained as follows：0.8% GW-1，0.2% resorcinol，0.4% urotropine， 0.2% acetic acid，0.3% thiourea and 0.02% modified nano-silica. The gelation time was 8 h，the strength grade of gel was G，and then the dehydration rate was less than 10% after aging 95 days at 130 ℃. The gelation time of gel was mainly affected by temperature. The higher the temperature，the shorter the gelation time was. The gelation activation energy of phenolic gel at 130 ℃by calculation was 88.2 kJ/mol. Compared with the non-toughened phenolic gel，the nano-silica toughened phenolic gel could increase the residual resistance coefficient of sand filling pipe from 88.3 to 963.0，the plugging rate from 98.9% to 99.9%，and the breakthrough pressure gradient of subsequent water drive from 3.45 MPa/m to 34.7 MPa/m. The amine modified nano-silica toughened gel gave the gel a suitable network structure，provided a support skeleton for the gel，and then enhanced its temperature and salt resistance，viscoelasticity and aging stability. The nano-silica toughened gel had good injectivity，long-term stability and plugging performance，which was suitable as a channeling sealing agent for offshore high-temperature and high-salinity reservoirs.