To reveal the time-dependent deformation and damage characteristics of the carbonaceous mudstone reservoir bank slope, using a low-field nuclear magnetic resonance test and triaxial compression rheological test, the pore evolution law and creep characteristics of carbonaceous mudstone under wetting and drying cycles are studied.On this basis, based on the damage theory and the Lemaitre strain equivalence principle, a creep damage equationconsidering the coupling effects of wetting and drying cycles, axial pressure, and time is established. The results show that as the number of wetting and drying cycles increases, the porosity of the carbonaceous mudstone increases, the pore structure changes from small pores to large pores, and the instantaneous strain and creep strain of the carbonaceous mudstone increase. The established damage equation can better characterize the influence of the number of wetting and drying cycles, axial pressure, and time on the damage evolution of carbonaceous mudstone. With the increase in the number of wetting and drying cycles, the damage of carbonaceous mudstone is greater, and the damage time effect is more significant. As the axial pressure increases, the rate of damage growth is fastened, and the duration of the accelerated damage is prolonged.