The dissolution separation of halite from rock salt and the mass transmisson of sodium chloride (NaCl) solution forming the dissolution process of rock salt are investigated. With the experimental studies of the dissolution characteristic of rock salt and the diffusion of sodium chloride (NaCl) solution. The changing regularity of the dissolution rate of rock salt and the separation coefficient with each primary influence factor,as well as the corresponding formulae are obtained. The dynamic differential equilibrium equations of rock salt solution are established.