Abstract: To investigate the intrinsic disaster-causing mechanism of slope instability, the weak interlayer, an important influencing factor, is studied. Taking charcoal mud shale with 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 visco-plastic body considering aging damage, a fractional-order creep model of charcoal mud shale considering aging 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 verified, and the model was subjected to parameter sensitivity analysis. The results show that the improved model has a better fit to the test data when compared with the traditional Nishihara model, and can completely characterize the decelerated, isotropic and accelerated creep stages of the carbonaceous mud shale, especially highly consistent with the characterization of creep curve in the accelerated creep stage. The variation of creep curves were controlled by parameters, while the material parameter reflects 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.