Abstract: Significant slide of rock layer occured during excavating foundation pit of a water power plant. In addition to large instantaneous deformation, the slide increased with time. Finite element analysis was adopted in this paper to simulate the whole excavation stage. The calculation results agreed fairly well with in-situ measurement including deformation and residual stress in rock.Rheological properties of rock is omitted in this paper and a subsequent article on this subject is now to be prepared.