The water conservation function plays a vital role in the land–water cycle. As the “Chinese water tower”, the headwaters of the Yellow River are of great significance to the safety of the Yellow River basin and even the global ecosystem. Taking the grassland ecosystem in the Yellow River source area as the research object, the InVEST water yield model with modified parameters and the ecological value evaluation of the modified equivalent factor method were used to explore the simulated spatio-temporal changes and the value of grassland water conservation from 2001 to 2020. The results show that: (1) the average total amount of water conservation in the source area is 549 × 10⁸ m³, which is 16% of the runoff in the Yellow River basin, with a growth rate of 7.5 mm/year 1 and a contribution rate of 30%; (2) the total ecological value of grassland water conservation in 2020 is USD 340.03 × 10⁸. The proportion of improved grassland in ecological restoration and management is only 0.51%, while the proportion of original alpine meadow reaches 67% and its ecological function and value are irreplaceable; (3) based on the comprehensive indicators of water conservation capacity, value and importance, Qumalai, Chengduo and Maduo counties are ranked as priority areas for the ecological protection of water resources.

Since the implementation of the grassland ecological protection policy of prohibition grazing on natural grasslands throughout the territory in 2003, the growth of grasslands in Ningxia has improved. This study investigated the spatial differentiation mechanism of normalized vegetation index (NDVI) in Ningxia grasslands from 1988 to 2018, analyzed the relative contributions of climate change (CC) and human activities (HA) to NDVI changes, and predicted the future trend of grassland changes. The results show that except in winter, the annual, seasonal and monthly average values of NDVI after grazing prohibition were higher than those before grazing prohibition. After grazing prohibition, the growth rate decreased by 17.91%, but the degradation rate increased by 3.92%. After grazing prohibition, the proportion of medium coverage increased by 16.15%, mainly in the path of “lower coverage grassland→medium coverage grassland”. The transformation trend was mainly positive, and the ecological construction project has achieved remarkable results. The main factors affecting NDVI differentiation in Ningxia grassland were snow depth, potential evapotranspiration, radiation, and precipitation. After grazing prohibition, the explanatory power of each factor and the interaction between the factors decreased significantly, but the explanatory power of wind speed was greatly improved. After the grazing prohibition, 53.22% of the total area was affected by human activities and climate change. The relative contribution of human activities decreased in NDVI-increased areas but increased in NDVI-decreased areas.