Abstract：Based on theory of plasticity kinetics，simply supported beam model of effect of anomalously low friction on rock mass was established considering deep coal mining. Through theoretical deduce，analytical formulas of normal stress of contact interfaces between rock and roof in elastic stage and elastic-plasticity stage under dynamic load were both presented. The relationship curves between q/p， and t were analyzed. The variation rules of friction on contact interfaces in rock mass were obtained. The effect of anomalously low friction on rock mass was explained on the basis of plasticity kinetics. The results indicate that normal stress of contact interfaces between rock and roof in elastic stage and elastic-plasticity stage reduced sharply under dynamic load. And the reduction amplitudes were relatively large. It is shown that friction on the contact interfaces reduced，which presented obvious effect of friction disappearance. Therefore，the existence of effect of anomalously low friction on rock mass was proved. Comparing normal stress of contact interface on elastic stage with that on elastic-plasticity stage，reduction amplitude of the former was larger，which illustrated that effect of anomalously low friction on contact interface between rock and roof was easy to occur when the beam was in elastic stage.
