Abstract: Experimental results on three coal samples of different coal ranks indicate that coal is one kind of rock that is of low sensitivity to temperature.The key factor that affects deformation mechanisms of coal-bed is temperature.As coal rank increases,plasticity of coal seam becomes weaker and its brittleness increases.Ductile mechanisms are dominated in the coal-bed of low coal ranks,but in the coal-bed of higher ranks brittle mechanisms are dominated.Strength characteristics of coal can not completely account for the phenomena that coal-bed is easy to flow strongly and to be detachment zone.Another factors need to be taken into account for these phenomena.