A detailed analysis is conducted on a severe storm occurred on 18 June 2005, combined the new generation radar data of Linyi with mesoscale numerical model outputs. The result shows that the strong convection weather process took place under the condition of dry and cold at upper levels and warm and moisture at lower levels, and the main factor causing this event is an asymmetric mesoscale vortex at 700 hPa. The hailfalling area was located at the southeast part of the vortex. The analysis of radar echoes shows that the strong centers were almost distributed vertically. During the hail process, the echo intensity increased, and the echo top and VIL (Vertical Integrated Liquid water) decreased quickly.