Abstract: Analyzing the characteristics of rainfall and runoff changes in the section from Hekou Town to Longmen Hydrological Station(Hekou-Longmen section), one of three major flood source areas of the Yellow River, is of great significance for flood control and drought resistance. This article uses methods such as mathematical statistics, moving average, and complete ensemble empirical mode decomposition (CCEEMDAN) to analyze and obtain the annual average rainfall of 457 mm and the annual average natural runoff of 4.593 billion m³ in the Hekou-Longmen section; Before the 1990s, the overall precipitation showed a decreasing trend, but after 1990s, it showed an increasing trend. The natural runoff has a periodic fluctuation pattern of 4 a and 9 a, showing a decreasing trend overall; The average annual rainfall runoff coefficient is 0.084. Affected by regional water and soil conservation construction, ecological environment improvement, and other factors, the annual rainfall-runoff coefficient in the Hekou-Longmen section shows a significant decreasing trend, from around 0.13 in the 1950s to around 0.05 in the 21st century. Due to the high summer evaporation, crop irrigation, and plant transpiration, the monthly rainfall-runoff coefficient from June to October is lower than that from November to May of the following year. The rainfall-runoff coefficient of each flood varies greatly in the Hekou-Longmen section.