In order to guarantee the long-term stability of silty mudstone in slope and tunneling projects, the DZSZ-150 multi-field coupling rock triaxial pressure testing machine was used to conduct creep tests on silty mudstone specimens of similar materials under different surrounding pressures. Based on the testing results, a nonlinear viscoelastic-plastic constitutive model describing the whole creep process of silty mudstone was established, and the proposed creep model was verified for its rationality and feasibility by taking the results at a confining pressure of 7 MPa as an example. It show that the steady-state creep rate of the specimen is related to the magnitude of the deviatoric stress, and with increase of the deviatoric stress, the steady-state creep rate and the deviatoric stress conform to an exponential function relationship; the creep rate in the accelerated creep stage is significantly greater than that in the decelerated creep and steady-state creep at low stress levels, and the creep damage occurs in a very short time; a nonlinear viscoelastic-plastic constitutive model is proposed to describe the whole creep process of the silty mudstone, which can describe the creep-deformation law of the whole process of creep-damage of silty mudstone, reflecting the creep characteristics of silty mudstone under different levels of deviatoric stress, and avoiding the problem that the classical model cannot accurately describe the accelerated creep process.