Abstract: After excavation of the dam foundation of Fenhe Reservoir 2,a dislocation of rock mass along bedding fracture plane is found.The dislocation, with displacements of 1 cm to 7 cm,spread on almost the whole dam poundation which is composed of hard dolomite of Cambrian system.In this paper,the dislocation of rock mass at the dam foundation is analyzed and studied. The dislocation is a result ofground stress release after the excavation of the dam foundation.