Abstract: Not only water injections into both fracturing and intact coal floor strata but also the physical simulations about these two kinds of floor reveal that water drain in the upper part takes place earlier than the lower part in bore holes and rocks in deeper part of coal floor break or fracture ahead of working face.In-situ measurements verify the above by observing the confined water intruding up into the coal floor,the protective strata,before mining.This paper considers the secondary stress as the condition of presssure water up intrusion.The water progressive intrusion is one of the theories about mechanism of water inrush.