Hong Kong Observation Operational Regional Spectral Model (ORSM) forecasting physical values in June and July 2002 were used to explore the large-scale atmosphere circulation situations and physical conditions causing continuously severe rainfall in the south of China by analyzing the features of average geopotential height field, temperature field, humidity field, meridional and zonal wind velocity field when heavy rainfall took place. The study of the thermodynamic and dynamical field near the heavy rainfall belt indicates that in temperature field, at the low and middle level of atmosphere, the heavy rainfall belt lies in the comparatively colder zone south of the high temperature zone with lower gradient, while the gradient is higher in the north of the heavy rainfall belt. On the other hand, in humidity field, the heavy rainfall belt is located in the high humidity zone, while at the low level of atmosphere, it is in the south of relative humidity gradient zone. Furthermore, in wind velocity field, at the low level of atmosphere, the heavy rainfall belt existed in the convergence zone of the east and west winds, south and north winds.