Abstract: The El Niño-Southern Oscillation (ENSO) is an important signal of global interannual climate change, and the East Asian Summer Monsoon (EASM) is the dominant factor contributing to summer precipitation anomalies in China, both are important climatic phenomena affecting hydrological processes at global and regional scales. In order to reveal the change characteristics of river runoff into the sea and its response to ENSO and EASM, this paper is based on the runoff data from 1960-2023 at the hydrographic stations of China's representative rivers-the Yellow River, Yangtze River, and Pearl River-into the sea, and applies M-K nonparametric tests, Morlet wavelet analysis, and other methods to analyze the trend and cycle of the runoff volume of the three rivers. Using M-K nonparametric test, Morlet wavelet analysis and other methods, we analyze the trend and cycle change of the runoff into the sea, and investigate the response of the change of the runoff into the sea to ENSO and EASM. The results show that the inflow of the Yellow River, the Yangtze River and the Pearl River show a significant decrease, a non-significant increase and a non-significant decrease in the trend changes, and the years of abrupt changes are 1985, 1988 and 2003, 1983, 1992 and 2002, respectively. The three major rivers have interannual cycles of 2~8 a time scale, and the response to ENSO is more and more significant from the north to the south; after entering the 21st century, the response of runoff to ENSO is not significant. There are interannual cycles of the Yellow River and Yangtze River runoff with EASM on the time scale of 2-6 a, but the Pearl River runoff has no significant resonance cycle with EASM; there is no significant resonance cycle of the three rivers' runoff with EASM on a long time scale (inter-annual). The results may serve as a scientific basis for the basin-scale water resources management, the flood/drought mitigation strategies and the region hydrological processes study.