Abstract: Successful numerical simulation output from WRFV2.2 combined with NCEP reanalysis data, observed precipitation data from automatic stations and Doppler radar reflectivity are used to analyze the heavy rainfall caused by typhoon Haitang in Zhejiang and Fujian provinces. The results show that the heavy rainfall is from the spiral clouds band close to the north of the typhoon center, and caused directly by the strong mesoscale convergence belt in the boundary layer. The rain belt develops and moves northward corresponding to the convergence belt. Three typhoon currents from different directions converge and ascend near the boundary of Zhejiang and Fujian provinces, transporting moisture and energy for the strengthening and maintenance of heavy rainfall. The confluence of these currents mainly happens in the boundary layer, which is the reason why the mesoscale convergence belt is confined in the boundary layer. The complicated mesoscale orography in Zhejiang and Fujian provinces plays an important role in the storm. The three different currents lift upward along the mountains ranging from north to south and trigger precipitation, which contributes to the heavy rainfall. However, the terrain plays no effect on the mesoscale convergence belt but prevents the precipitation from extending westward.