Based on the conventional observations,NECP/NCAR reanalysis data,automatic weather station intensive observations and Doppler radar data,this paper contrasts the two typical squall line processes in Jiangsu and its surrounding areas on 28 Apirl 2006 and 14 June 2009.Results show that,prior to the two squall line processes,the warm advection obviously occurs in the lower troposphere and the cold advection appears in the middle-upper troposphere,which is helpful for the formation and development of stratification instability.During the movement and development of squall lines,a clear convergence line occurs in the surface wind field,which plays an important role in the triggering and maintenance of the squall lines.There are obvious differences of thermal and dynamic structures between the environment fields of the two processes.For the thermal structures,the former happens in spring when cold air is still strong and warm advection in the lower troposphere is one of main reasons of stratification instability,and the latter happens in summer when warm moist air is active and cold air invasion in middle-upper troposphere deserves attention greatly.The dynamic analysis shows that low level convergence and lifting conditions of the former are better than those of the latter.However,the thermal conditions of the latter are predominant,and it is easier to develop once the convection starts.