Abstract: The mushroom cloud forming in a very short time after blasting and the overflwing gases from the heap that emited very slowly from the heap made up the amount of the explosive gases. According to their movement characterstics, the mushroom cloud was taken as the souce of instantaneous volume and the overflowing gases from the heap was taken as the irregular volume, their diffusion pattern is selected as the pattern of smoke volume integral. On the basis of consideration, the pollution evaluation pattern of an open-pit was established by simplifing the pattern and amending the diffu-sion coefficient. A reltively accurate pollution prediction on explosive gases in Dayie Iron Mine was carried out.