Abstract: Safety monitoring results of a dam with clay core are presented. As the left abutment of the major dam is very steep, the TStype displacement transducers and GKDtype pore water pressure transducers are installed to monitor the displacement and seepage of the joint part of clay core and the abutment. The results show that although the stability of the slope of the dam satisfies the criterion, significant displacement and seepage occur at the interface between left abutment and clay core.Therefore, in designing the bank slope of the dam, special attention must be paid to prevent the displacement and the crack resulted.Seepage at key parts in the dam should be observed. Moreover, in numerical analysis of the dam by finite element method, two set of material constants should be chosen to signify the saturated and unsaturated situations corresponding to construction period and water storage period. 