<p>Predicting the onset of accelerated creep remains a key challenge for describing the full time-dependent deformation of rocks under sustained loading. This study conducts triaxial progressive loading creep tests to obtain axial strain evolution under different stress levels and develops an improved creep-damage constitutive model to overcome the inability of the traditional Nishihara model to capture accelerated creep. The Perzyna rate-dependent viscoplastic formulation is embedded into the Nishihara framework, and statistical damage theory is introduced to define stage-transition thresholds associated with micro-defect accumulation. Model parameters are identified by least-squares fitting, and the proposed model is validated against triaxial creep curves. The results show that the improved model reproduces the stage-wise creep behavior (decelerating, steady-state, and accelerated stages) and provides a physically interpretable criterion for the transition into accelerated creep. The proposed framework offers a more reliable basis for long-term deformation prediction and creep-related risk assessment of rock.</p>