The circulation features and its formation cause in Shanghai in 1999 were investigated,including mei-yu quantity,mei-yu period,the beginning and ending of mei-yu,and its relationship with the subtropical high,East Asian summer monsoon intensity index,the convective activity in tropical zone and typhoon were discussed.The results show that the intensity of subtropical high is weaker,the ridge line of subtropical high is leaning to south and east,the East Asian summer monsoon intensity index is weaker and begins earlier,ITCZ is not active,typhoon sums are less,and they are the formation factors of the mei yu anomaly in Shanghai in 1999.