Gravity dam foundation failure progress is always associated with its deformation development. So dam foundation deformation should be paid more attention in gravity dam stability analysis. Key node plays an important role in analyzing the dam foundation deformation development. But how to select key node is worth researching. A gravity dam foundation stability is studied by the development of plastic zone and key nodes’ displacements in dam foundation. The problem of key node selection is researched and a key node selection method is brought up also in this paper.