Since high depth,large disharge,heavy working strength and non-suspension of navigation as the predominant factors to the TGP(Three Gorges Project)river closure,all the means and measures will be adopted to reduce the difficulty on the river closure and Phase-2 construction.Therefore,the tasks such as hydrometric measurement,hydrometeorological forecast,hydrographic surveying,hydrological analysis/calculation and hydraulic computation are important conditions for the successful river closure with high quality.This paper deals with the hydrological technical issues in river closure and Phase-2 construction,and points out the corresponding ways.