Abstract: On the basis of the fracture distribution of coal-rock mass, infiltration flow mechanical characters and the mechanism of grouting to block up flow, the paper analyses the reasons of formation and classification of infiltration water fractures, and the mechanism of cracked coal-rock mass’s grouting to cut-off water, and discusses the relations between permeability coefficient, stress and temperature, between water pressure and grouting pressure and between groutability of rockmass, grouting position and drill hole depth. At last, the paper alanyses a project example that describes grouting to cut-off the flow in the roof of an air intake roadway of southern part of Yanliu Mine, the result indicates that, through grouting into surrounding rock with low fracture level in depth, a grout curtain to cut off infiltration flow might be formed, and that a fallback grouting from deep to shallow into cracked roof with abundant water was conducted, thus, the effect of above two kinds of grouting was obviously improved, at the same time, the consumption of raw material and project cost were reduced.