The relationship between 10—30 d low-frequency oscillation and the rainfall over Changjiang-Huaihe River Valley during Meiyu period is analyzed by using the 756 stations' daily precipitation data in China and the NCEP/NCAR daily reanalysis data from 1961 to 2010.The results show that a 10—30 d periodic variation is obvious in the flood years during Meiyu period.The activeness and break of rainfall over Changjiang-Huaihe river valley during Meiyu period is also closely associated with the low-frequency oscillations' northward and westward propagation.During Meiyu period in flood years,the rainfall over Changjiang-Huaihe river valley is influenced by the low-frequency anticyclone over the South China Sea and the low-frequency cyclone over the Sea of Japan in the lower troposphere,which modulate the western North Pacific subtropical high to extend westward or to retreat eastward,and thus affect the water vapor transport and confluence of cold and warm air in Changjiang-Huaihe river valley.In the upper troposphere,the low-frequency anticyclone and cyclone in mid-latitude area over Asian mainland influence the position of South Asian High,which leads to the intensity changes of low-frequency rainfall over Changjiang-Huaihe river valley.