Abstract: Based on the reanalysis data with a spatial resolution of 1.0°×1.0° from the National Centers for Environmental Prediction (NCEP),the atmospheric circulation data of 2.5°×2.5° from the National Oceanic and Atmospheric Administration (NOAA) and the assimilation data of 1.0°×1.0° from the Global Data Assimilation System (GDAS),and using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model,the characteristics of water vapor transport were analyzed for two landing typhoons "Jelawat" and "Haikui" that had similar tracks but large difference in precipitation distributions and the effect of water vapor on increase of heavy rainfall after landing weakness of the "Haikui" typhoon was discussed.The results showed that the maintenance duration and precipitation of "Haikui" after landing are stronger than those of "Jelawat" after landing.Water vapor transported from the inland (59.9%) plays an important role for "Jelawat".Without water supplement from the ocean,"Jelawat" declines rapidly and the precipitation intensity decreases.After the landing of "Haikui",water vapor is mostly transported from the South China Sea and Yellow Sea,which can come from two paths,one from the eastern ocean surface that travels directly into the rainfall area and the other from the southern region related to the tropical cyclone (TC) circulations.Water vapor during the first heavy precipitation event after the landing of "Haikui" is mainly coming from the ocean in the east of Japan (61.2%),and water vapor transported from the South China Sea contributes the enhancement of the second heavy precipitation event to a certain extent.Water vapor during precipitation in the southern region of Jiangsu province is mainly from the East China Sea and East China (46.3%).Water vapor and energy in the East China are both smaller than those from the southern warm ocean,and water vapor decreases gradually during long distance transportation,which probably results in the weak precipitation in the southern region of Jiangsu province.