Through analyzing the result of uniaxial and triaxial creep tests on rock salt from Yunying and Jintan salt mine and mudstone from Jintan salt mine

the effect of external conditions concluding stress state and confining pressure and internal construction on the creep characteristics of rock salt are studied. No matter under any confining pressure

the steady state creep rate of rock salt increases obviously following the accreting detective stress. Confining pressure

which plays a role of restricting creep deformation

however

has a little effect on the steady state creep rate more and more as confining pressure increases. Furthermore

larger grain size and more inclusions in the rock salt will result in weakening creep property. In this paper

the origin and the nature of this internal stress

which develops during inelastic deformation of the material

are discussed. It is shown that this internal stress

which reflects the microstructure evolution of the material under the competitive action of hardening and recovery mechanisms and bridges the gap between micro construction and macro experimental phenomenon，can serve as an internal state variable in the creep constitutive model of rock salt. Good agreement between the numerical results obtained from the model presented and experimental data of creep curves to triaxial multi-grade compression test is given.