The initiation, development and evolution of the squall line on Sep. 8th,2002 over central part of Yunnan Province are analyzed by using the surface observation and radar echo data. The result shows that the weather and physical factors as follows: the thunderstorm occurred, the humidity rose rapidly, and the temperature lapsed when the squalls occurred over the low latitude plateau. The strong wind, heavy rain and hail occurred, and the pressure was discontinuons during the chopping process. The length of squall line is less than 100km and the width is only about 10km. The life time of the squall is about 2 hours. Before it occurred, the radar echo had certain premonitory and changing character.