Abstract: In order to investigate the intrinsic disaster-causing mechanism of slope instability, the weak interlayer, an important influencing factor, is studied. Taking charcoal mud shale weak interlayer as the main research object, the graded shear creep test of charcoal mud shale was carried out to reveal its creep law and determine its long-term strength under different normal stress levels. By improving the traditional Maxwell body, replacing the traditional viscous element with a fractional-order element, and introducing a viscoplastic body considering ageing damage, a fractional-order creep model of charcoal mud shale considering ageing damage was established; based on the optimized Levenberg-Marquardt method of 1stOpt software, the experimental creep curves of the charcoal mud shale were fitted, and the accuracy of the model was The accuracy of the model was verified, and the model was subjected to parameter sensitivity analysis. The results show that compared with the traditional Nishihara model, the improved model has a better fit to the test data, and can completely characterize the decelerated, isotropic and accelerated creep stages of the carbonaceous mud shale, especially the accelerated creep stage of the creep curve of the characterization of the high degree of agreement; the creep curve changes by the parameter \gamma ,A,\nu control, the material parameter A and \nu reflect the physical and mechanical strength of the carbonaceous mud shale. The results of this paper can provide some theoretical basis for the slope stability analysis of the soft and weak interlayer containing carbonaceous mud shale.