Abstract: In order to solve the wedge pillar type goaf of the coal mining face with a hard roof affected to the mining in the upper seam, based on the description on the rheological features of the coal pillar with the general Kelvin Body, a dynamics model of the coal pillar-roof system was established. In combination with the min pot ential energy principle, an effective loading time calculation formula of the coal pillar in the goaf was obtained. An analysis was conducted on the formula affected to the factors of the coal pillar effective loading time and finally in combination with the engineering cases, verifications were conducted. The results showed that the coal pilla r-roof system of the goaf would be steadily in failure and instability with the time passed. The effective loading time of the coal pillar and self viscosity cofficient would be in a positive linear relationship, would approximately be in a " parabola" relationship to the instantaneous elastic cofficient, would be in a positive proportion relatio nship to the cross section area and would approximately be in a negative index relationship to the long term elastic coefficient, roof rigidity and coal pillar height. The es tablished mechanics model of the goaf coal pillar-roof system based on the rheological features of the coal pillar could derive the calculation formula of the coal pillar ef fective loading time with certain accuracy.