The planetary scale system and synoptic scale system such as blocking high and West Pacific high during the continual rain in flood season by using the data from 1960 to 2000 are analyzed. The distribution of dynamical and thermal character of continual rain is obtained after analyzing the physical quantity fields with five-year T106 data. A middle-range prediction model for continual heavy rain in flood season with the help of ECMWF numerical forecast data. And the result is fine after two-year application.