By using the precipitation data from May to August(1951～1987)at 34 stations in the upper and middle reaches of the Changjiang River and maximum entropy spectrum method of the moving sample series,an objective and detailed study is performed on the periodic oscillationfeatures of the wet season precipitation in the reaches,Results show that there is an obvious quasi-biennial oscillation in the data.In addition’we study the distribution of the oscillations.The other periedic oscillations are not so obvious and stable.