A synthetic analysis of heavy rainfall event of typhoon Tailim depression in Jiangxi Province during 2—4 Sep. 2005 is made with the dense observational data and NCEP re-analysis data. The results show that the weak cold air invading to the typhoon depression led to the strength of energy front in PBL when the typhoon depression is steady in northwest of Jiangxi. The development of continental high in West China retarded the westward moving of typhoon depression. A weak environment stream field provided a good condition to its maintaining long time and staying in northwest of Jiangxi. The sustained vapor transport and divergence of NE cold current from the cold front in meddle latitude and SE warm flow from ocean in low latitude were helpful to the severe torrential rainfall event as the good dynamical and thermal conditions to the typhoon depression in low tropospheric levels. It was demonstrated that the orographic effect contributed greatly to precipitation enhancement due to orographic lifting and convergence with intensified precipitation on the windward slope of the Dabie mountains and Lushan mountain as well as Jiuling mountains.