It is shown that the relationship between the phase of 50 hPa QBO in winter and the summer drought/flood trend in the lower and middle reaches of Changjiang River is characterized by very marked stages. For the entire period of 1953-1989, the relationship between them is very weak. But according to the data they could be devided into three stages.The relationship in each stage is very strong.And the anomalous evolution of 50 hPa QBO is examined that shows to be related properly with the stratifying of the three stages.