The stream function and potential function of water vapor transport vector dur ing a heavy rainfall in the Huaihe River valley in the summer of 2005 is studied and the averaged water vapor budget is computed and diagnosed during the event period. The results indicate that the main water vapor source of the event is the strong vapour transportation band coming from Philippinesand across South China Sea and arriving to the middleeast China. This strong vapor tran sportation was composed of two branches. The first one was from Pacific vapor tr ansport center and it moved westward along the south region of equator. The othe r one was coming from the easterly trade wind in the southern hemisphere which got across the equator at Africa's Somalia peninsula and then arrived to the nor th of Bangal Gulf, and finally reaching to Philippines. The area of severe vapor transport vector converge corresponds with the area of the heavy rainfall. The total water vapor budget corresponds with the average rainfall, the average rain fall increases with the increasing total water vapor converge. On the other hand , the water vapor vertical transport at low level corresponds well with the avera ge arearainfall.