During the periods when the summer low-level convergence zone and convective activity in the Tibetan Plateau are interrupted, the daily variable plain-mountain thermal circulation on the east slope of the Plateau causes the development of convectional systems in the slope region. This is one kind of the mechanism that results in generation of meso-αscale convective cloud clusters is Sichuan basin. When these meso-αscale convective cloud clusters entered the complex topographic region in the middle reaches of Changjiang River, the more complicated meso-scale convective organization appeared and alternation of weakening and strengthening occurred. In macroscopic view, sometimes they stagnated and sometimes leaped down stream. When the convective precipitation in Meiyu front cloud zone is activated and strengthened gradually, a cold band and the corresponding thermal front emerged in the lowest layer, and when a strong meso-αscale cloud cluster with heavy rain developed up, a wave train which is composed of three or four meso-αscale clusters with heavy rain formed in the middle and lower reaches of Changjiang River through a quick adjustment process. As some meso-αscale convective cloud clusters, which are initiated in the low-level unstable region in the south side of Meiyu front, came into Meiyu zone, strong meso-αscale cloud cluster may developed up more easily.