Based on the conventional observations andNCEP reanalysis data, the two similar storm cases occurred on June 30 and July 21, 2008 in Longnan disaster areawere diagnosed. The analytic conclusions are as follows: The shearing low vortexwas themain influence system of“6. 30”heavy rainfal,l but less ascendingmotion resulted in less stations’s precipitation up to 50 mm. The plateau low vortexwas themain influence system of“7. 21”storm rainfal,l because ofbettervapor condition and strong vertical ascendingmotion,the precipitation in 50 percent stations ofLongnan region wasmore than 50 mm during“7. 21”storm rainfal.l The relation is in evidence between the loss from heavy rainfall disaster and the center area of rainfall