Provided is a using method of a water blocking device for a grinding machine. The water blocking device is formed by a storage box, a spring device, a water blocking steel sheet, a locking device, a magnetic block and a hook. The water blocking steel sheet is pulled out of the storage box, the hook is hung at a corresponding portion of the periphery of a grinding wheel of the grinding machine, the magnetic block is attracted to the corresponding portion, above the hook, of the grinding machine, the locking device is pushed to press the water blocking steel sheet in the storage box tightly, and the water blocking steel sheet stretching out of the storage box is made to be tightly attached to the periphery of the grinding wheel of the grinding machine. The problem that operation is influenced by the splash of grinding fluid is solved effectively, the circulation using of the grinding fluid in the grinding machine is ensured, the occurrence of accidents due to the fact that the grinding machine is made to carry static electricity by accumulated water is avoided, the working efficiency of operating workers is improved, working yield is improved, and the production cost of enterprises is lowered.