Abstract: The analysis of the characteristics of flood in the Yongjiang River shows that the floods almost occur in July-September,the later rainy season in the southern China,and its variations correlate closely to the summer precipitation in the Yongjiang River drainage area by using the data sets of the flood peak and the annual highest water levels of the river,and the monthly precipitation over every observatory in the river drainage area.In this work,we analyse the climatic conditions causing flood in the Yongjiang River based on the NCEP/NCAR reanalysis data and the Outgoing Longwave Radiation(OLR) data.The results are as follows:(1) The flood in the Yongjiang River is mainly caused by Tropical Cyclones.When the West Pacific Subtropical Anticyclone is more northward than usual,ITCZ(intertropical convergence zone) can more easily affect the Yongjiang River drainage area,associating with the frequency of Tropical Cyclones and the activity of convection.(2) Landform makes an important contribution to the flood of the Yongjiang River.(3) The flood occurs easily in negative sea surface temperature anomalies(SSTA) over the eastern equatorical Pacific.We also analyse the variation of the synoptic systems cuasing the flood,and changes of the annual highest water levels in the condition of climate warming to futher realize the climatic reasons causing the flood.