Abstract: The Meiyu process in the middle and lower reaches of the Yangtze river on 22 June 1999 was analyzed in this paper using the dense observational data and the high-resolution out put of numerical simulation.The results show the heavy rainf all process was due to some meso-γ-scale disturbances formed in the mesoscale convergence line almost simult aneously in the boundary layer.Such meso-γ-scale vortex was located in the boundary layer initially,and the duration is a fewhours.The clarity of the cyclonic circulation is also different in the boundary layer,the cyclonic circulation of the disturbance in this paper is mostclear at 0.91 sigma level.