Functional zoning diversifies the management of grazing intensity within protected areas (PAs). However, the complexity makes it difficult to assess grazing intensity and thus understand the effectiveness of PAs in reducing grazing intensity. In this study, grazing intensity in Madoi County, the Yellow River source region, was evaluated based on mapping gridded livestock in areas where grazing was permitted under management measures in functional zones. The effectiveness of PAs in reducing grazing intensity was then assessed by comparing the changes in grazing intensity in PAs and non-PAs. Furthermore, the contributions of climate change and grazing activity to vegetation changes were quantified using temperature (°C), precipitation (mm), grazing intensity (sheep units/ha), and the normalized difference vegetation index (NDVI) (a proxy of vegetation cover) data. Subsequently, the effects of reducing grazing intensity on vegetation changes were analyzed by comparing the contribution of grazing activity to vegetation changes inside and outside of PAs. The results showed that the average grazing intensity in PAs decreased by 0.23 sheep units/ha, which was higher than the decrease in non-PAs (0.07 sheep units/ha) as expected. Specifically, the average grazing intensity in the core, buffer, and experimental zones decreased by 0.36, 0.22, and 0.14 sheep units/ha, respectively, any of which was a greater reduction than that in non-PAs. The contribution of grazing activity to the increase in vegetation cover in PAs was 12% higher than that outside of PAs, indicating that the positive effect of grazing activity on vegetation changes in PAs was greater than that outside of PAs. The findings suggest that the establishment of PAs in the Yellow River source region are effective in reducing grazing intensity and enhance the positive role of grazing activity in vegetation changes. Our research provides a reference for analyzing the effectiveness of functional zoning in areas with large-scale grazing livestock.