The conventional observation, weather satellite, and NCEP/NCAR reanalysis data are used to perform the dynamic and mesoscale analyses of the rare mountain flood in history in Lushi County in the western Henna Province from 28 to 30 July in 2007. The results show that the subtropic high over the West Pacific enhanced and overlapped on the Begal high and thus resulted in a blocking pattern; the lowlevel jet with a large amount of water vapor converged around the strong frontogenesis field in the west of Henna, which led to the occurrence of the extreme rainstorm. In the strong inclined ascending motion area, there was a conditional symmetric unstable mechanism at lower levels, which caused the occurrence and development of the mesoβ clouds, and consequently induced the rainstorm.