Abstract: Using the HYSPLIT v4.8 model and the NOAA atmospheric circulation (2.5°×2.5°) and NCEP GDAS (1.0°×1.0°) data, the authors investigated variations in water vapor transportation features and the contribution of water vapor to their major pathways from Tropical Storm Bilis (0604).The authors classified the data into two phases:pre-rainstorm and post-rainstorm.The results indicate that the entire Bilis life cycle has four major water channels:Somalia, the Bay of Bengal, a cross-equatorial flow at 120°E, and the eastern Pacific water vapor.The data was then further classified into two reversed categories:the first is the southward water vapor transported from Somalia and the Bay of Bengal, which plays a key role in moisture transportation; the second is the cross-equatorial airflow at 120°E and the flow from the eastern Pacific, which results from the interaction between the cyclone and the southwest monsoon and enters a rain belt northeast of the circulation center.The southern water vapor channel from the Somali jet and the Bay of Bengal is related to the southwest monsoon and transports moisture up to levels of 850 hPa.The South China Sea and the western Pacific transports moisture to levels greater than 850 hPa.Comparing the water vapor contribution rate of each channel before and after increased rainstorms, it is observed that the low latitude water vapor, formed due to increased rainstorms in the Bay of Bengal, plays a significant role in the formation and development of the increased moisture during torrential rain.