Based on the meteorological data and the Doppler radar data of Hefei, general circulation background, echo's development and evolution of the hail during 21 May 2004 in Chaohu, Anhui Province are analyzed. The results show that continued hail along the Chaohu lake in the short time period is closely related to its position between land and lake and caused by the superposition of mesosystem and the land and lake breeze.