The mechanism of creep from the perspective of internal energy is analyzed. Based on the strain energy theory

a creep constitutive model is established by combining the Perzyna viscoplasticity theory and Nishihara model

which can describe the whole process of transient creep

steady state creep

and accelerated creep. The model takes into account the influence of stress state on the accelerated creep

and defines the critical strain energy density to effectively judge the occurrence time of accelerated creep. On the basis of the unified creep constitutive model

a practical simplified creep constitutive model is built by adopting Drucker-Prager yield criterion and associated flow rule; and using the yield stress ratio to reflect the creep strain rate change of accelerated creep

which can predict the accelerated creep and reflect the whole process of the three stages of creep. As the simulation result is basically consistent with the test data

the research results provide a new idea for the study of rock creep fracture process.