The following are the main characteristics of the general circulation of atmosphere in May 2012:there is only one polar vortex center in the Northern Hemisphere with stronger strength than normal years. More troughs occur in middle high latitudes in the Asian area, and lead to several cold air currents to influence China. The subtropical high is slightly stronger than normal years. The East Asia major trough is clearly stronger than usual at the same time period. The south branch trough at 90°E is slightly stronger than normal years. The monthly mean temperature averaged over China is 16.8℃， which is 1.0℃ higher than the same period of normal years. The mean precipitation (66.1 mm) is 2.63% more than normal(64.4 mm). There are 5 precipitation processes in May 2012. Extreme precipitation events occur in Provinces Gansu and Hunan, and drought is mitigated in Yunnan. High temperature occurs in Sichuan, Yunnan, Guizhou and Guangxi. Strong wind and hail disasters hit many regions in China in May.