The climatic characteristics and causes of hazy weather in Wuxi, Jiangsu Province, are analyzed based on surface observations obtained from Wuxi Meteorological Office from 1980 to 2011 and Wuxi Statistic Yearbook data from 1991 to 2011. The results show that the number of haze days in Wuxi is in an increasing trend, especially in the late 5 years. The haze days appear most in winter, followed by spring, autumn and summer in succession. The haze processes that last for 10 consecutive days all go through high pressure, the rear of high pressure moving to the sea and the ground inverted trough. The air masses in middle and low levels are seen sinking in the back trajectories simulation during 10 consecutive days of haze and the extremely haze events, and the areas the air masses pass have higher pollutant concentration. The key factor for haze events in 1990s is the dust emission in industrial pollution, and then since 2004 industrial waste gas and vehicle exhaust increase year by year, causing the haze days to increase as well.