In order to expand the application range of flexible graphite gasket in harsh working conditions, polytetrafluoroethylene (PTFE)was selected as impregnating agent, and flexible graphite gasket was modified by liquid phase impregnation method. The optimum impregnating agent ratio and impregnation process were determined by single factor condition experiment. The results show that the best impregnation effect can be obtained under the conditions of impregnation vacuum degree of -0.095 MPa, vacuum pressure of 0.65 MPa, impregnation times of two times, impregnation time of 30 min, impregnation concentration of 60% (mass fraction) and impregnation temperature of 35 ℃, and the leakage rate of impregnated flexible graphite gasket is 2.03×10-4 cm3/s, the weight gain rate is 4.39%, the compression rate is 32.17%, and the rebound rate is 22.34%. SEM and EDS test results show that polytetrafluoethylene emulsion penetrates into the gaps between graphite lamellae through impregnation, effectively filling the gaps between lamellae and particles in flexible graphite gasket, and improving the leakage of gasket. Carbon element is mainly distributed uniformly in the form of graphite, oxygen element is distributed uniformly in graphite as impurities, and fluorine element is concentrated.