Based on the new generation weather radar data in Guilin, a severe squall line event ahead of a front occurred in Guangxi on 5, May 2005 is analyzed to study the evolution of the squall and its convective cell. The results show that this squall line is a combination of follow-up type and consecutive type. The meso-scale convective cell in squall line causes severe convective wind. Before convective cell move into squall line, it can become a mature supercell with TBSS and BWER features. The vertical accumulated liquid water content can get 70kg·m-2, and produce local great hail. Based on the VIL value, the location of most severe strom can be found and the heavy hailstorm can be identified, the nowcasting of severe convective weather can be made.