Based on creep test results insitu and in laboratory on granite of Three Gorges Project(TGP), the viscoelastic numerical simulation on excavation process of the underground hydropower plants was performed by using the generalized Kelvin model as viscoelastic model of ranite.The calculation results show that the deformations of the surrounding rock mass increase by 5 to 10 percent when its creep characteristics are considered,and the deformations of rock mass under each excavation step may last 7-10 days and approach tostability. 