Red mudstone in central Yunnan has significant rheology properties, which can bring hazards to the engineering construction. Using step loading shear creep experiments, the shear creep characteristics of the red mudstone, which from ShiziShan tunnel section, were investigated. The results showed that, the rock samples mainly exhibited decay creep at smaller stresses, while it would undergo the whole process of creep from decay creep, steady creep to accelerate creep damage at larger stresses. Regression analysis was conducted on the deformation data of each stage of the rock sample, and a fitting equation was established, and it was found that the deformation of rock samples at each stage was nonlinear. In accordance with the nonlinear deformation properties of the rock sample, an exponential acceleration element was proposed. By connecting with the viscous element in the Bingham body, a modified Bingham body was formed. It can overcome the shortcomings in acceleration phase simulation of the traditional Bingham body. Additionally, the nonlinear improvements were made to the Hoke and Kelvin body. By series connecting the nonlinear Hoek body, Kelvin body and the modified Bingham body, a nonlinear and unsteady viscoelastic-plastic rock creep model, which can describe the creep characteristics of the red mudstone in central Yunnan, was established. The results from the theoretical model were in good agreement with the experimental data, indicating that the proposed model was reasonable.