The attenuation of natural

γ

-radiation of shales passing through coal medium in mine was studied using Monte-Carlo method. The intensities

energy spectra

and angle distributions of

γ

-radiation on the surface of coal seams with different thicknesses were calculated. The attenuation of

γ

-ray in this case was found to be different from that in the case with narrow monoenergy beam. The total intensity of

γ

-rays decreases obviously with the thickness up to 20 cm

and slowly above the thickness. But the intensity for

γ

-rays in low energy region changes still rather obviously even for greater thickness.