Based on the monthly precipitation data of 160 stations and daily rainfall data of 753 stations provided by the National Climate Center of china,the daily global OLR(outgoing long-wave radiation) data from National Oceanic and Atmospheric Administration,and the NCEP/NCAR reanalysis data,this paper studies the characteristics of low frequency oscillation of summer precipitation and convection over the Yangtze-Huaihe basin during the drought/flood and drought-flood-coexistence(DFC) years.Results show that summer rainfall over the Yangtze-Huaihe basin has multi-scale periods,which are remarkably different in drought/flood and DFC years.The 8—16 d quasi-biweekly oscillation(QBWO) plays an important role in drought years,while the 16—32 d period and QBWO are found to coexist in flood years.The 16—32 d oscillation also occurs in DFC and common years,accompanied with comparatively weak QBWO,which seems more significant in DFC.Thus,QBWO may be regarded as a vital factor for summer rainfall variation.On the other hand,the oscillation period of OLR is highly correlated with that of summer rainfall.As regard to the propagation of low frequency convection,it is found that the 8—16 d(16—32 d) low frequency convection mostly propagates in the southward(westward) direction in the typical drought(flood) years.