Abstract: El Niño-Southern Oscillation (ENSO) is a crucial signal of global interannual climate change, while the East Asian Summer Monsoon (EASM) is the dominant factor causing abnormal summer precipitation in China. Both are important climatic phenomena affecting hydrological processes on global and regional scales. To reveal the variation characteristics of river runoff into the sea and its response to ENSO and EASM, we analyzed the trends and periodic variations of runoff from three representative major rivers in China (the Yellow River, Changjiang River, and Pearl River) based on data from their estuarine hydrological stations (1960~2023). Methods including the Mann-Kendall non-parametric test and Morlet wavelet analysis were employed for this purpose, and the response of runoff changes to ENSO and EASM was explored. The results indicated that: ① The runoff into the sea of the Yellow River, Changjiang River, and Pearl River showed a significant decreasing trend, an insignificant increasing trend, and an insignificant decreasing trend, respectively. The abrupt change years occurred in 1985 for the Yellow River; 1988 and 2003 for the Changjiang River; and 1983, 1992, and 2002 for the Pearl River. ② All three rivers exhibited interannual periodic variations in runoff into the sea on a time scale of 2~8 years, with the response to ENSO becoming more significant from north to south. However, the response of runoff into the sea to ENSO has been insignificant since the 21st century. ③ The runoff into the sea of the Yellow River and Changjiang River had interannual periodic variations with EASM on a time scale of 2~6 years, while the Pearl River showed no significant resonant period with EASM. Additionally, there were no significant resonant periods on a long-term (interdecadal) scale between the runoff into the sea of the three rivers and EASM. The research findings can provide a reference for watershed water resources management, drought and flood prevention, and regional hydrological process research.