Abstract: Daily and hourly air quality index (AQI) data from October of 2012 to May of 2015 in 11 cities of Zhejiang province were used to analyze the occurrence time,durations and temporal variations of AQI during the 61 severe air pollution events when the AQI was more than 200.Weather patterns were used to reveal the spatial-temporal variations of severe air pollution events as well.The results show that severe pollution events mainly occur in winter,especially during December and January,and PM_2.5 is the primary pollutant.The number of severe pollution hours is more in the northwestern region than in the southeastern region,appearing significant regional differences.Three types of weather patterns contribute to severe pollution in Zhejiang province and they are Synchronous Change,North-south Transport and Regional Accumulation.Type North-south Transport can be further divided into Movement Transport and Diffusion Transport with the former presenting local movement and area movement patterns.Type Regional Accumulation tends to develop into severe pollution with long-hour duration.