Abstract: A case of heavy rain (1989) and a case of extremely heavy rain (1982) in the middle reaches of Yangtze River are analysed, respectively. They were associated with two kinds of low vortexes during the mei-yu period. The genesis and evolution of the two kinds of mei-yu vortexes and the accompanied torrential rain development processes are studied. One is the typical southwest vortex, it likes a weak baroclinic cyclone, but its baroclinoic structure is generated in the dynamic-thermal process of its own genesis and development in the subtropical warm environment. Another is the small-size positive vorticity disturbance traveling through the mei-yu shear line, its evolution process is more complicated. According to the two cases, some previous results from the authors themselves are verified, substantiated and summed up in this paper. And, some difficult points of the forecasting of complicated heavy rain development processes are discussed.