Analyses of some aspects,such as the relation between heavy rain and flood, the atmospheric circulation and the meso-scale system about the typical flood-causing heavy rain process in QingJiang Valley in the first and the second dekad of august in 1998 are made. The results show that, flood peaks in QingJiang Valley are formed straight from flood-causing heavy rain and the total times and frequencies of rain clusters are closely related to the accumulating area averaged rainfall of the heavy rain process. Generation of the flood causing heavy rain is closely related to the situation of the subtropical high over the west Pacific at 500hPa, and the meso scale systems and their dispositions and evolutions in upper, middle, and lower layers.