Due to the enormous disaster of the heavy rainfall in Hunan and Guangd ong, etc., caused by the severe landing tropical storm Bilis, the process is inv estigated based on the dense observational data, the satellite data, NCEP/NCAR r eanalysis data and products of MM5. The results show that the tropical depress i on moved tardily owning to the surrounding of the west Pacific subtropical high, north mainland high, Tibetan high and low latitudes high. The southeast stream from the southwest part of the subtropical high and the southwest monsoon stream transported the vapor to the depression continuously, which was propitious to t he maintenance of its intensity. It is found that plenteous vapor, intense verti cal convection and strong convergence of the low level stream have advantage for the heavy rainfall by analyzing MM5 numerical forecast products and physical factor field.