Meiyu onset over YangtseHuaihe river valley is of obvious features of interannual variations. Based on NCEP/NCAR reanalysis dataset and NOAA OLR an d ERSST data, the previous stronger signal of anomalous Meiyu onset over Yangtse Huaihe river valley is investigated by employing correlation and composite analy ses. Preliminary analyses for the impact of the stronger signal on the Meiyu ons et are also studied. The results show that ENSO(Southern Oscillation) events are the previous stronger signal. The Meiyu begins late (early) with the warm (cool) phase of ENSO. The SSTA of Nino4 in February and spring can be regar ded as credible implications for forecasting the onset of Meiyu. The weak convective activ ities around the AsianAustralian “land bridge", Philippines, the western Paci fi c warm pool and Indian peninsula correspond with the warm phase of ENSO. The wea k convective activities around the regions abovementioned may not facilitate n orthward jump of the western Pacific subtropical high and the outbreak of Indian summer monsoon . Consequently, the seasonal transition of atmospheric circulation in the easter n Asian regions is late, which causes the late onset of Meiyu.