Abstract: In this article we analyze the abnormal severe rainfall in Ningbo triggered by weakened landfalling Typhoon "DuJuan"(1521) in Fujian using routine observational data, AWS data, satellite data, radar data and NCEP reanalysis data. The heavy rainfall in Ningbo was caused by the convective development of clouds associated with the weakened typhoon on the edge of the enforced westward moving subtropical high. The rainfall is accompanied by strong lightning characterized with low centroid precipitation. The large-scale sustained water vapor supply by low-level jet stream is a necessary condition for precipitation. The negative value, minimum are the beginning of incease of water vapor flux are 12 hours ahead of the beginning, increasing and end of heavy rainfall. The gradient and location of the energy field are good indications for the prediction of typhoon rainstorm. Heavy rainfall occurs 12 hours after the appearance of large gradient area in the energy field. Heavy rainfall occurred under the condition of convective instability, accompanied by the development of the horizontal component of the moist potential vorticity associated with the warm and wet flow, riggering the increase of vertical vorticity. The location and intensity of the meso-scale convergence line is an accurate indication for precipitation of the next hour.