The existing phenomenological constitutive model is hard to describe how the impurity content

temperature and strain rate affect the mechanical behavior of the salt rock. It is more difficult to explain its deformation mechanism. Salt rock mainly consists of halite crystal. The deformation mechanism of salt rock is controlled by the polycrystalline structure. Therefore

it is more appropriate to build the plastic constitutive model using solid dislocation theory for the description of the deformation of the rock salt. The mesoscopic mechanism of the plastic-creep is the coupling of dislocation sliding of inner crystal grains and dislocation climbing-sliding of boundaries and their interference surfaces of inner crystal grains. According to the above hypothesis

the relationship between the average scale of the subgrain (or grain) and flow stress

the mean density of dislocation of inner grains and evolution model of microscopic parameters (including dislocation

subgrain diameter and boundary width between subgrains) are obtained sequentially. Finally the meso-macroscopic deformation and then plastic constitutive equation of salt rock are established using Orowan’s law. The obtained equation can reflect the physical mechanism of plastic-creep deformation of salt rock and has an improved physical significance

comparing with traditional plastic constitutive model. This constitutive model could only be obtained through observation and research on mesoscopic structure of rock salt.