Abstract: A severe chilling damage that was the widest range and the largest temperature decreasing rate since 1974 took place in the middle,north and east area of Yunnan.It belongs to abnormal event in warm climatic background.From January to July,northern Hemisphere 100hPa and 500hPa height fields warm were more similar those of leading to high temperature of Yunnan in August.As a result,the chilling damage in August was very difficultly predicted.During the chilling damage,the high and middle latitude on 100hPa and 500hPa were dominated by meridional circulation.Yunnan province located behind trough and before riddle and was controlled by northward wind.On 70hPa,Yunnan province was controlled by southward wind.So there was obviously vertical wind shear between the upper-level and the low-level,which provided dynamic and moisture condition for the chilling damage.At the same time,the maintenance and continuous complement of northern cold air were important conditions which cause the chilling damage in August 2002 take place.