Exploring strategies for sustainability is an urgent issue for policy-makers to meet the grassland resource needs of wild ungulates and livestock. From the perspective of grassland food supply and consumption, an evaluation system for grassland food supply service and ecological spillover values was established in the Yellow River Source National Park (YRSP) of the Three-River-Source National Park. The compensation value of grassland ecological spillover and the ecological-economic value of wild ungulates were calculated. Results showed that: (1) There were 39.55 × 10⁴ Standard Sheep Unit (SSU) of livestock and 8.24 × 10⁴ SSU of wild ungulates in the study area. Among these, 90.24% of livestock and 44% of wild ungulates were distributed in the Traditional Utilization Zone (TZ) and Other Human Activity Zone (OZ). (2) The grassland food supply value was $255.59 million. The ecological spillover value of the grassland food supply was $79.75 million; a positive value indicating a state of ecological surplus. The ecological-economic service value of wild ungulates was $1.09 billion. (3) The ecological spillover value of the grassland food supply was -$13.43 million in Huashixia due to the large number of Pseudois nayaur living there. One solution to this conflict would be reducing the number of livestock, for which ecological compensation of approximately $13.43 million could be achieved. On the other hand, the feed intake of livestock could also be reduced by providing an external supplementary feed. About 1.91 × 10⁴ SSU of livestock needed to be fed supplementary, and this was equivalent to approximately 7.54 × 10⁴ t of forage.