Abstract: In this paper the relation between dielectric constant and frequency is studied by using fractal geometry theory.The results show that the dielectric constant of coal has fractal characteristic,and the relation between the practical part of dielectric constant and frequency is:ε′_r (f)^∝f^d-D/2.Dielectric fractal dimensions of 11 coals have been obtained,and they are relative to content of pyrite sulfur,heat and ash content for coal.