Abstract: NCEP 11Reanalyzed data,TBB black bright temperature data,auto station hourly precipitation data and Mesoscale Numerical Model MM5（V3.6）were used to Simulate the Extra Torrential Rain Event Happened on June 25th,2010 in Qujing Malong of Yunnan Province.Mesoscale Features And Forming Reason of this storm rainfall event were analyzed mainly from aspects of motivational structure and instability mechanism.Results indicated that,stronger vapour convergence column existed in lower layers during the period of precipitation.Before the strong precipitation,intense convective instability energy assembled in lower layers at which the forming of sudaerial convergence lines lead to convergence.Because of intense vertical ascending motion,strong convective instability energy released quickly which contributed to intense convective precipitation.The structure of divergence in higher layers and convergence in lower layers was beneficial for the maintaining of vertical ascending motion and precipitation.Terrain sensibility experiment indicated that,the location of subaerial convergence line implicated to the terrain of Yunnan,and therefore influenced the position of convective storm rainfall.