According to the fact that the sandy rock mass exposed to the natural environment is susceptible to water and soluble chemical attack, the triaxial shear test is carried out on sandstone specimens treated with CaCl₂ reagent with different pH value. The second-order simplified generalized Kelvin rheological model conforming to the experimental rule is chosen to deform it into three stress states according to the hypothesis of the Poisson's ratio. Based on the least squares method (LSMPS) of the search pattern, the optimal solution of the model parameters is obtained, and the sensitivity of the model to the change of the parameters is evaluated by the root mean square error. The delay time is used to evaluate the time required for the sandstone to stabilize the creep process in different chemical environments. The model parameters identified by the search pattern can make the calculated value of the model close to the measured value obtained by the loading test, which indicates that the model and its parameter identification method are suitable for determining the rheological characteristics of the sandstone under the disturbance of chemical factors.