Considering difference between water and the other spectral characteristics and FY-3/MERSI channel spectral and spatial resolutioncharacteristics, this paper presented a method of detecting water and water change information using FY-3/MERSI. Taking Huaihe River Basin asa case, FY-3/MERSI was used to monitor the water body change before and after the precipitation process at the end of June to the middle of July,2016. The monitored results were verified using 50m -spatial -resolution GF -4 satellite. At last, the further development direction by usingsatellite remote sensing technology for monitoring water body change was given.