The correlation analysis is made between the May mean rainfall over Lijiang from 1971 to 2000 and the height fields of 100 hPa and 500 hPa during the same time.It is found out that the main influencing weather systems influencing rainfall in May in Lijiang include the 100 hPa South Asia high,500 hPa South Sea subtropical high,low system over the Bay of Bengal,and Xinjiang high(ridge) at mid-high latitudes.Through abalysing the observed and anomaly fields in May 2005 at 100 hPa and 500 hPa,it is shown that the circulationpattern causes of the drought persisting from spring to summer in May 2005 include the strong the subtropical high over the South Sea,the weak low over the Bay of Bengal,and the weak-than-normal South Asia high and Xinjiang high,which together obstructed the confluence of the Southwest Monsoon cloud cluster and the cold air from noth over Yunnan,so to result in the severe drought.