Water disasters in coal mining often bring a variety of huge losses, but it is difficult to monitor water seepage in coal mines. Based on the principle of optical fiber microbending loss and the optical time domain reflection(OTDR) technology, this paper presents a method of detecting and locating mine water seepage. Combined with the water expansion characteristics of expansive soil waterproof mat (GCL), GCL in the water seepage zone expands and conducts deformation to the fiber tightly attached to the outer diameter. The detection results of water seepage can be obtained through the principle of optical fiber micro-bending loss. At the same time, combining with the principle of OTDR, the deformation point of bending loss, namely the water seepage point, can be positioned. The experimental shows that the seepage location is basically consistent with the measured results and the method has a good location effect.