[Objective] To reveal the hydrological regimes and trends of runoff and sediment discharge in the mainstream of the upper reaches of the Yellow River. [Methods] Using the non-parametric Mann-Kendall test, Pettitt′s test, and Morlet wavelet transform, this study analyzed the trends, abrupt changes, and periodic variations of runoff and sediment discharge in the upper mainstream of the Yellow River from 1950 to 2020. [Results] The annual sediment discharge varied significantly at different stations in the upper mainstream of the Yellow River compared to the annual runoff. The maximum annual average runoff and sediment discharge were observed at Xiaheyan Station, reaching 304.74×10⁸ m³ and 1.13×10⁸ t, respectively, while the minimum values were recorded at Tangnaihai Station, being 203.67×10⁸ m³ and 0.12×10⁸ t, respectively. The annual runoff was mainly concentrated in the Xiaochuan-Shizuishan section, while the annual sediment discharge was mainly distributed in the Xiaheyan-Toudaoguai section. Both annual runoff and sediment discharge at all stations showed a decreasing trend and had significantly decreased from 1990 to 2020. Notable abnormal changes in runoff and sediment discharge were observed in 1968, 1985 and 1986. There were 2-5 obvious peaks in runoff and sediment discharge as shown by wavelet analysis, indicating that there were multi-time scale characteristics in the evolution process of runoff and sediment discharge. The fluctuation amplitude of wavelet coefficients of runoff and sediment discharge showed a continuous decreasing trend, and the periodic characteristics of both the runoff and sediment discharge also exhibit a weakening tendency. In the future, both runoff and sediment discharge are expected to continue decreasing, with the decreasing trend of sediment discharge being more significant. [Conclusion] The results highlight that human interventions, such as the construction of cascade reservoir groups, comprehensive watershed management measures, and the continuous increase in water withdrawal outside the river channel, have become the dominant driving factors for the variations of runoff and sediment discharge processes in the upper mainstream of the Yellow River. The findings of this research will offer valuable insights for guiding watershed water resources planning and efficient management in the upper reaches of the Yellow River.