Abstract: Technical water supply system of hydropower plant is used to cool the generator and bearings. Taking Manwan Hydropower Plant as a case, the emerged problems of technical water supply system of generator were analyzed. Due to out of sync of water supply systems with unit's startup and stop, the water supply system supplies water ceaselessly, wasting water seriously. Through analysis, the measures was determined, i.e, adding a motor operated valve behind the water supply filter of the main water supply pipe and connecting the controller with run-stop process of the unit. One-year operation of the renovated water supply system has proven that the technical water supply system operates normally and reliably, hydraulic loss reduces obviously, and the automatic level of the plant is improved.