The mudstone has low bearing capacity and low per Zelin meability, which experiences large deformation and long-term creep. To investigate the creep characteristics of the Tianshui Landslide, Gansu Province, China, triaxial creep tests were conducted. It is shown that the creep behavior of mudstone became more pronounced as the confining pressure, water content, and shear stress level increased. The long-term strength of the mudstone decreased as the creep time increased. A new creep model for the mudstone is proposed. The values predicted by the new model are in good agreement with the test results. The axial strain in the mudstone samples exhibited a linear relationship with time in a log–log graph under different stress states; the strain increased slowly with time and gradually stabilized. The model reflects the residual creep characteristics of the mudstone and can reflect both axial and volumetric creep. Moreover, the microscopic mechanism of clay creep was studied by analysis of scanning electron microscope images. This study considered the actual engineering situation, and the experiment was designed to study steady creep of mudstone under low confining pressure and variable water contents, with the aim of establishing a stable creep model to characterize the mudstone under low confining pressure. The stress–strain–time model of creep deformation of mudstone established herein has few parameters and a simple derivation process and provides new information for evaluating slope long-term stability. The model will be useful for the prediction of mudstone landslides in the Tianshui area.