Abstract: Extreme humid-heat events directly impact human health and socio-economy. Extreme humid-heat events in summer in China mainly occur in the southeast region. The results of this study show that the relationship between early winter El Ni?o and Southern Oscillation (ENSO) and summer extreme humid-heat days (EHHD) in southeast China during 1961-1993 is weak, while the relationship between ENSO and EHHD during 1994-2020 is significant positive correlation, and the increase of EHHD caused by El Ni?o events is the main reason for the enhanced correlation. In the latter period, when the El Ni?o events occurred in the early winter, the western North Pacific anomalous anticyclone (WNPAC) was westerly and stronger in summer, and the sinking motion, downward shortwave radiation and water vapor transport anomalies caused by it were conducive to the increase of EHHD. Further analysis shows that the WNPAC intensity is closely related to the El Ni?o decaying pace. In the latter period, the El Ni?o events decayed more rapidly, leading to significantcold sea surface temperature (SST) anomalyin the equatorial central-eastern Pacific and warm SST anomalyover theMaritime Continentin the following summer. The cold SST anomaly in the equatorial central-eastern Pacific excited an anticyclonic Rossby wave to its west, while the warm SST anomaly over the Maritime Continent triggered eastward-propagating Kelvin wave and strengthened the meridional Hadley circulation, collectively enhancing the WNPAC. In addition, the mid-latitude circumglobal wave train caused by tropical SST and its accompanying precipitation anomalies is conducive to the formation and maintenance of WNPAC. In contrast, in the previous period, the El Ni?o events decayed more slowly, resulting in weaker summer SST anomaly and WNPAC anomaly, which had an insignificant impact on EHHD.