The use of gel plugging is an important technology for achieving balanced displacement and enhancing oil recovery in high water cut reservoirs. Under the conditions of high temperature and high salinity reservoir，the stability of the gel deteriorates， and it is easily broken through by subsequent injection fluids under production pressure differences，resulting in a low gel plugging rate. Therefore，it is necessary to propose effective ways to improve the performance of the gel. In the article，micrometer sized fly ash was added into the gel system，by the measurement of the rheological property of the gel system，the injection performance， gelation time，high-temperature stability，and fracture stress of phenolic gel system filled with fly ash was investigated. The results showed that when the amount of fly ash was 1%—2%，the viscosity of the gel forming solution was 20.6—33.4 mPa s，exhibiting good pumping performance. The gelation process was slightly delayed，with a 2—4 hour extension of gelation time at 90 ℃ and 150 ℃. The high-temperature stability of the gel system was significantly improved，and the stability time at 150 ℃ was extended from 20 days to more than 120 days. The storage modulus of the gel increased from 7.4 Pa to 25.2—49.8 Pa，while the fracture stress remained almost unchanged with the amount of fly ash used. The addition of fly ash could effectively improve the thermal stability and plugging strength of the gel. In field experiments，fly ash enhanced gel has shown good water control and oil incremental effect.