Based on the April temperature data of 20 surface meteorological stations of the Beijing region from 1990 to 2004,the characteristics of Beijing spring urban heat island(UHI) were analyzed.The results show that the UHI in the nighttime was stronger than that in the daytime.Furthermore,with the additional data from three automatic meteorological observing stations and the 325m meteorological tower of LAPC(State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry),the characteristics and influencing factors of a strong UHI event on 18th-19th April 2003 were analyzed.And the results show that the strong UHI event occurred in the nighttime of 18th,and its centre lay over major urban area along the Baijiazhuang-Tian'anmen-Gongzhufen area,it weakened and disappeared in the next daytime,and the diurnal change of the strong UHI was very obvious.In the clear night of sunny day on 18th,the surface wind speed over the urban areas and the suburb was very small(≤1.0m/s),and the wind speed below 15m in the surface layer remained weak(≤1.5m/s),and the strong inversion in the atmosphere layer below 320m maintained all the night,and all of these contributed to the formation and maintenance of the strong UHI.And in the next daytime the solar radiation had most important effects on the weakening and disappearance of the strong UHI,it made the suburban surface atmosphere temperature rise faster and more than the urban atmosphere temperature and the urban surface inversion temperature as well as strong UHI disappear in the end.