A process of severe convection occurring in Shanghai on August 25,2010 is analyzed by using LAPS(local analysis and prediction system) analysis field to assimilate various meteorological data.Results showed that the storm was trigged directly by mesoscale convergence systems on middle and lower layers.The convergence lines on surface developed into strong ones in the formation stage and became the major triggering mechanism of the mesoscale vertical circulation.In the meantime,the vertical structure contributed to the mesoscale convection development because of the convergence on middle layer and the divergence on high layer.The prominent updraft zone located near the storm center,and the relative humidity grew significantly on middle and high layers.In the mature stage,the downdraft drag,which occurred on low layer near the storm centre,made the updraft more slantwise.The mesoscale circulation structure and moisture supply were destroyed in the decaying stage,and the vertical structure was contrary to that in the formation stage.The LAPS analysis field has an advantage in spatial and temporal resolution,which well revealed the spatial structure and development process of meso and small scale systems in the mesoscale analysis.