Abstract: By use of the 20 MN servo-controlled triaxial rock testing machine with high temperature and high pressure in China University of Mining and Technology,an experimental study is carried out on creep properties of large size granite specimens of Φ200 mm×400 mm with temperature up to 600℃ and axial stress up to 175 MPa.Through the analysis of experimental data,it is discovered that hydrostatic stress can cause creep formulation of lu gray granite.A constitutive equation of stable-state creep rate considering hydrostatic stress is thus proposed.The creep constitutive equation parameters of lu gray granite A1,A2,ΔQ,m,n are obtained.It is discovered that the creep properties caused by hydrostatic stress are the same as those caused by the differential stress in lu gray granite.It can also be divided into three stages: transient creep,stable-state creep and accerlerating creep.The creep formulation of lu gray granite is a function of temperature,differential stress and hydrostatic stress.Increase of temperature,differential stress and hydrostatic stress can accerlerate the creep formulation of lu gray granite.  Creep constitutive relationship of lu gray granite under high temperature and three-dimensional stress