Abstract: The paper deals with the variation of the physical and mechanical property of coal mass after vibrating. The method of fractal geometry is applied to quantify the regularity of crack change in coal mass before and after the vibration.It is found out that the fractal dimension becomes larger after the vibration,which shows the crack number increases,and that the increase of the fractal dimension will tend to be stable after vibration of the coal mass for some time.The compressive stength,the elastic modulus and the descending modulus will get smaller after the coal mass is vibrated.The longer the vibrating time or the higher the original stress level is,the more obvious the effect of the vibration on the mechanical property of the coal mass will be .