Abstract: Based on the daily temperature data measured in Chongqing from 1961 to 2016, the variation trend and characteristics of urban heat island effect in the past 56 years was analyzed. At the same time, based on the hourly temperature data from 2009 to 2016, the daily change of urban heat island effect was analyzed. The results showed that in the past 56 years the urban heat island effect of Chongqing had an upward tendency. In each season, the most obvious rise was in midsummer season. There were obvious seasonal variation of urban heat island effect of Chongqing. In midsummer the urban heat island effect was the strongest, it was the second strong in early spring, and it was the weakest from middle spring to early summer. There were obvious daily variation of urban heat island effect of Chongqing. In each season, urban heat island effect was strong in the day and weak at night. The urban heat island effect of Chongqing was determined by urbanization process factors such as urban underlying surface change (area and distribution of green space and water), air pollution, anthropogenic heat emission and so on. It also influenced by natural factors such as geographical position and meteorological condition. Combined with the characteristics of Chongqing city, there were some measures to reduce the urban heat island effect.