The main river closure for construction of the Three Gorges Project (i.e. TGP) on the Yangtze River is a complicated systematic engineering with deep water, large discharge, strongly riprapping and keeping navigation during closing the stream. In the process, hydrologic and sediment monitoring has been employed to observe water-silt variation and underwater topography, and provided a scientific decision basis for optimizing the construction schemes. It has also been used for providing the prototype observation data for the channel diversion, keeping navigation,protecting cofferdams during flood season, hydraulic experimental study as well as hydrologic forecasting and calculating. This paper shows reader the case of the monitoring, the instrumentation and technology used for hydrologic data collection, transmission, procceding during the river closure.