AbstractUsing National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis and other data, a joint monsoon index IEAAM is defined for capturing variation features of East Asian summer monsoon and Australian winter monsoon as an entity. The East Asian–Australian monsoons (EAAM) are found to be stronger after 1993 whereas weaker before this year. When EAAM is anomalously strong, cold sea surface temperature anomalies appear around north coast of Australia, facilitating easterly wind near equator to strengthen in lower troposphere and both the Australia High and the northwestern subtropical anticyclone to intensify. The divergent flows emanating from the Southern Pacific Convergence Zone (SPCZ) region and tropical north Pacific, respectively, force Australian High and northwestern Pacific subtropical anticyclone to reinforce. The anomalous convergence around Kalimantan Island links East Asian monsoon to Australian monsoon via the divergent flows. During strong EAAM years, rainfall is surplus over south coast of China and southern Japan whereas deficient over northwestern tropical Pacific and southwestern tropical Indian Ocean.