Abstract: The Dongfanghong gravity dam, which has been worked for forty years, has serious cracks, leakage and carbonization now. Its uplift pressure is increasing by years. By use of observation data of piezometric level on the dam base surface, the statistic model has been built up for the piezometric level, and an inverse model has been developed for seepage parameters according to the observation data of piezometric level and seepage flux. The seepage and uplift at dam foundation were analysed. The safety evaluation was performed for the seepage conditions.