Numerical simulation and terrain sensitivity experiments on the heavy rainfall caused by the typhoon Nesat during 29-30 September 2011 were studied using the weather and research forecast(WRF) model when Nesat made the landfall and went through the north Hainan Island. The results show that: The rainfall caused by the westing typhoon landfall on the north area distributed more in the north than the south. In the north, there is more rain in the west area than east area. 48 h and 3 h accumulative rainfall from the 12 km experiment are successfully modeled and the landing time and location is close to the observed. The typhoon track and intensity are good simulated as well. The terrain sensitivity experiment shows that 24 h precipitation from the experiments with terrain have increased generally by more than 50 mm in the west area in Hainan Island. Increase of more than 150 mm has been observed in the western mountainous regions, with 350 mm increase in the north part of the main peak. Heavy precipitation center is found responding to main mountain peak, It proves that, the terrain can result in general obvious rainfall increase in typhoon. However, there is a 50~150 mm rainfall reduction in the eastern coast of the island due to the block from the Wuzhishan Mountain. Analysing the comparison of low-level mesoscale flow field and the vertical velocity, significant difference can be found between control experiments and experiment with none terrain. The Wuzhishan terrain can enhance low-level disturbances, which can easily produce the vortex of mesoscale convection (MCS), then by increasing the typhoon rainfall. The special terrain of Wangxia plays an important role in increasing the typhoon rainfall.