Abstract: Based on the data of drilling, geophysical exploration and roadway fault exposure of No.3 upper 107 working face in first mining area of Sanhekou Coal Mine, the water bearing capacity of Sanhekou fault and Qianzhai fault in natural state is analyzed, and the fault sealing methods such as lithology juxtaposition map, SGR method and fault plane normal pressure method are used to evaluate the fault water conductivity in natural conditions from lateral and vertical aspects. The numerical simulation of fault seepage characteristics and activation law under the condition of mining in working face is carried out. The results show that both Sanhekou fault and Qianzhai fault are water free faults under natural conditions. When the working face is excavated 30 m away from Sanhekou fault and 26 m away from Qianzhai fault, the pore water pressure in the two fault layers increases slowly, and only the upper end of the fault is damaged within a small range, and the overall water blocking performance of the fault does not change.