Abstract: A severe squall line event was studied based on conventional observation data,automatic weather station data,GFS analysis data at spatial resolution of 0.25° and temporal resolution of 6 h,and observations of Doppler radar and radar wind profiler in eastern China on 4 March 2018. The results demonstrate that it was a rare,severe squall line with features of untimely occurrence,fast moving,wide range and catastrophic damages during early spring (late winter). It originated and evolved in the divergent area of the upper air jet,in front of the low level southwesterly jet axis and in the warm area of a low level vortex. Meteorological elements varied fiercely during this process. The large horizontal temperature gradient formed by the surface cold pool and warm air ahead of the squall line enhanced the intensity of the system. The severe thunderstorm high,the strong pressure gradient and fast moving of the strong squall line resulted in extremely damaging gale,which was further intensified by the bow echo,the supercell,and downward transport of momentum. The effects of special terrain (such as the smooth lake and trumpet-shape topography) were also favorable for the formation of the gale.