According to statistics

the eighty percent of water inrushes and submerged well accidents were induced by the faults in China. Most of them were induced by the fault activation affected by the workface advanced in non-water-transmissible faults under the condition of original geology. Owing to the need of safe production and water-preserved mining

the activation and water inrush of faults in overburden rock due to the advance of workface were analyzed with mechanics. The mining methods of both preventing fault activation water inrush and water-preserved mining were researched. The fault activation criterion was deduced by the Mohr-Coulomb failure criterion. The calculating formula of critical obliquity and the critical mining depth of the fault activation were deduced. The calculating formula of critical advanced distance was deduced in activating of the fault for the interval mining method adopted. The results show that the failure form of the fault has prodigious relation with the obliquity of fault. With the increase of fault obliquity

the failure form of fault show successively: simultaneity failure of the fault with overburden rock in advancing of the workface

shear failure and tension failure. The more the increase of fault obliquity becomes

the easier activation of fault becomes. According to research result

the critical advanced distance was calculated when the interval mining method adopted

following the example of water-preserved mining at Daliuta mine. The calculated result was validated by the use of a similar simulation.