Abstract:By using the NCEP/NCAR reanalysis monthly data during 1979-2011, the monthly mean sea surface temperature data from Hadley center and precipitation data from 160 stations of China, the causes of severe rainfall over the Yangtze River basin in summer of 1998 were analyzed. Results demonstrate that a southwest-northeast abnormal heating gradient set up because of the positive anomaly of diabatic heating of Indonesia area and negative or slightly positive anomaly diabatic heating of its northeastern ocean areas, which makes the lower atmosphere convergent and the higher one divergent in Indonesia, and verse visa in tropical western Pacific, so a southwest-northeast vertical circulation circle was formed. Lower abnormal divergence of the tropical western Pacific air flow can be considered as abnormal vorticity source, which forced the anticyclonic circulation to occur in South China Sea. Moreover, the convergence of perturbation energy from the north side of Indonesia in South China Sea area is benefit for the maintaining of the abnormal anticyclonic circulation in South China Sea. The anomalous south wind flows in the western flank of the anti-cyclonic circulation brought abundant moisture to Yangtze River basin where the convergence of water vapor occurred, inducing strong rainfall there.