Abstract: Based on 500 hPa geopotential height fields and mean position of East Asian trough, a definition of the East Asian winter monsoon index(I₅₀₀)is given.The analysis ofI₅₀₀that the winter monsoon undergo a pronounced reduction during the past 50 years.Since the year of 1987, the winter monsoon has become rather weakened.Using the seasonal precipitation data of 48 stations in Guangdong from 1954 to 2004, the grades of drought and flood from April to June are marked off and analyzed by the regional drought and flood index (W-index). Results show that there are nine severe flood years and ten severe drought years in the past 51 years.The effect of abnormal w inter monsoon on the precipitation from April to June is obvious.The strong East Asian w inter monsoon usually leads to severe drought.