Abstract: By using synoptic charts,hourly GMS5 infrared TBB pictures and Doppler radar echo data,the rainstorm process on August 16,2003 has been analysed.The results show that there is an obvious mesoscale character of the rainstorm in spatial and temporal distribution.The macroscale synoptic situation supplies suitable circulation background,instability condition,energy condition and dynamical condition for the forming and development of the mesoscale system.The shear cloud system develops into a squall line.And the three mesoscale α cloud clusters and one mesoscale β cloud cluster aroused by the shear cloud system produce the heavy rainfall by analysing satellite cloud pictures.The mesoscale β shear line between east wind and west wind and the contrary wind are very important to the forming and development of the mesoscale α squall line by analysing the Dopplar radar echoes,arousing a supercell and a vmaxmesocyclone,and the mesoscale α squall line directly produces the rainstorm process.