Abstract: By employing a numerical typhoon model with a horizontally three-layer overlapped and two-way nested structure,two numerical experiments with true sealine and with extended sealine in the southeast of China have been carried out to investigate the effect of distribution of the sealine on the amplifying of the torrential rain of the landing tyhoon 9216. The results show that the convective precipitation caused by the dynamic lifting of the orography plays an important role in the amplifying of the rainstorm of the landing typhoon. The centre of the rainstorm moves with the extended sealine and the rainstorm can occur on the extended land. The lower extention of the sealine has little effect on the path of typhoon but has some effects on the intensity and the easterly jet of typhoon. The amplitude of the rainstorm weakens due to the decreasing of the orographic precipitation resulted from the weakening of the orographic acclivity. Therefore,the dealing of the orography in the model must be careful considering the probable amplifying of the rainstorm of typhoon caused by the small modification of the orography.