The present invention provides a coal mine underground reservoir storage coefficient measurement device. The device comprises a test case internally provided with a similar simulation material rock, one side of the test case is connected with a water duct, the other side of the test case is connected with a water outlet pipeline, the water duct is connected with a water storage sump, the water duct is provided with an electric control automation water check valve, the water outlet pipeline is connected with a water storage capacity monitoring device, a compression plate is arranged at the top of the test case, the compression plate is connected with a compression rod, the compression rod is hinged at a lever, one end of the lever is hinged on a support frame at the upper portion of the test case, the other end of the lever is connected with a compression device, the compression device is provided with a pressure monitoring device, the support frame is provided with a displacement monitoring device to monitor the displacement amount of the compression plate, and the electric control automation water check valve, the water storage capacity monitoring device, the pressure monitoring device and the displacement monitoring device are connected with a computer. The coal mine underground reservoir storage coefficient measurement device can really simulate the water storage mined-out area top board pressure environment and measure the storage coefficient under the effect of the top board press so as to greatly improve the reliability of the water storage capacity prediction of the mine underground reservoir.