This paper discussed the probability and variability risk of water inrush from No. 9 coal seam floor during mining under high pressure. The grey一risk model is used to calculate and evaluate the risk base on the statistical data about water levels of existing bursting points, maximum water yield and specific capacity discharge. It is concluded that the risk is very great to mine the lower group coal seam under the high pressure in Guoerzhuang mine. The author proposes that the measures, including mining by areas and mining一detecting, should be taken in advance to reduce accident emergency.