Abstract: In view of the abnormal roof water inrush of 8101 working face of Wolonghu Coal Mine caused by casing broken, numerical simulation method was used to analyze the mechanism of water inrush. By numerical simulation, the changes of stress and displacement of the surrounding rock of gas drainage hole was analyzed with the working face advancing. The results show that the roof stress appeared three stress reduced substantially points and the displacement increased synchronously and separation developed when the working face passed the gas drainage hole 10 m; when the working face passed the gas drainage hole 20 to 30 m, the stress achieved the largest decline and the displacement increased substantially then the stress and displacement changed a small margin. It's a good corresponding with the roof abnormal water inrushing phenomenon. The results show that sandstone fracture water flows to the working face from the broken casing because of the casing broken.