Abstract: It is found that uplift pressure measured at main dam foundation since 1994 is relatively high in many dam sections, especially at sections No.8, No.9 and No.10. It was not only of high uplift pressure, but also of great seepage quantity, the coefficient of uplift pressure was up to 0.97. The uplift pressure and seepage quantity measured at No.8 and No.10 are abnormal due to the close relationship between reservoir stage and foundation drain hole and result in great pitfalls. Supplementary treatment for main dam body foundation is carrying out at presently. Something has been done which revealed the abnormal to remove the high uplift pressure and great seepage quantity.