Abstract: In order to reflect the whole process of soft rock creep, the red mudstone creep experiment is carried out. The experimental results show that the elastic modulus gradually decreases with the increasing time and the viscosity coefficient gradually increases with the increasing time under the constant stress before yield. Therefore, this paper argues that the processing method of creep damage in the traditional theoretical rheology is not applicable to the damage evolution of the viscous coefficient, and the fractional calculus is used to describe the viscoelastic and viscoplastic strain of soft rock creep. By constructing an elastic body based on time-dependent damage, which is in series with a viscous body and a viscoplastic body based on fractional calculus, a new nonlinear creep damage model is established. The creep test data of red mudstone, frozen soft rock and red sandstone are identified with the creep damage model of soft rock, and the rationality and applicability of the proposed model is shown.