Abstract: The source region of the Yellow River is a typical alpine ecologically fragile region in China. It is imperative to study the spatio-temporal changes of ecosystem services and their tradeoff/synergy relationships for ecological security and sustainable development in this region. Therefore, in this paper, InVEST model was used to quantify four ecosystem services − water yield, soil conservation, carbon storage and habitat quality in the source region of the Yellow River from 2000 to 2020. The Spearman correlation coefficient method was used to analyze the relationship between ecosystem services, and Getis-Ord Gi* statistical index was used to identify the cold/hot spots of ecosystem services. The trade-offs and synergies of ecosystem services were spatially expressed using GeoDA software for binary local spatial autocorrelation analysis. The results are as follow: (1) From 2000 to 2020, water yield and soil conservation in the source region of the Yellow River showed a fluctuating trend of "increasing, then decreasing and then increasing", while overall, they showed an upward trend with an increase of 139mm and 43.2t/hm². The carbon storage and habitat quality showed a slight decreasing trend of 0.4% and 1.9%. Spatially, water yield and soil conservation exhibited a distribution pattern of "higher in southeast and lower in northwest". The high-value areas of carbon storage and habitat quality were predominantly located in the central part of the study area. (2) In the source region of the Yellow River, the hot spots area of ecosystem services had the largest proportion of forest land and grassland in the middle of the study area, while the cold spots area was mainly distributed in the source area above Zhaling Lake and Eling Lake and in the northern part of the study area. (3) There was a trade-off relationship between water yield and habitat quality, and the weak trade-off relationship between water yield and carbon storage turned into a weak synergistic relationship in 2020. There was a synergistic relationship between water yield and soil conservation, carbon storage and soil conservation, carbon storage and habitat quality, as well as soil conservation and habitat quality. Trade-offs between ecosystem services were weakened and most synergistic relationships were enhanced. (4) In terms of spatial pattern, there was significant spatial heterogeneity of ecosystem service trade-offs and synergies. High-high synergies were mainly distributed in the central part of the study area, while low-low synergies were mainly located in the western and northern regions. Low-high trade-offs and high-low trade-offs were mainly dispersed in the central and northern regions as well as the southwestern part of the study area.The research results are expected to provide guidance for the optimization of ecosystem service spatial pattern and the construction of ecological civilization in the source region of the Yellow River.