Abstract: Based on the monthly and pentad average TBB data of 17 years,and the data of 500 hPa height departure fields averaged by pentad in Eurasia,the standard deviation of TBB was calculated month by month over South China Sea,and its spatial-temporal distribution feature was analyzed.Meanwhile,the characteristics of TBB intraseasonal oscillation and its Longitudinal propagation feature was analyzed by means of the band-pass filter over South China Sea in the drought year(1985) and flood years(1991,1998) in Changjiang and Huaihe River basins.The results indicate that the oscillation of TBB 30～60 d and 10～20 d over South China Sea is very active in the flood years in Changjiang and Huaihe River basin,and the northward propagation is very clear.When the strong convection phase of TBB is propagated to the subtropical zone around 30 °N,it strengthens the convection disturbance in the subtropical zone,and leads to a period of intensive rainstorm.It is contrary in the drought years.Finally it was revealed that the structure of the wave train is of great difference in the drought years from the flood years in Changjiang and Huaihe River basins by the teleconnection between the convective activity over the South China Sea as well as 30 °N district and the 500 hPa height departure fields averaged by pentad.