According to the mechanical properties of coal-rock in accelerated creep phase, the generalized elastic-viscoplastic model of coal-rock has been modified through substitution of the non-liner Newtonian element for linear one, then the constitutive equation of the modified model and its creep equation in simple stress conditions have been derived. Finally, the cure fitting of experimental data has been made by use of the creep equation, and the creeping parameters of coal-rock have been gained. Through comparing the results obtained from theoretical analyses with experimental ones, the advances of the modified model have been confirmed.