Ecosystem multifunctionality (EMF) plays an irreplaceable role in maintaining ecological balance and ensuring human survival and development. However, few studies have focused on the effects of different grazing intensities on EMF, and little is known about changes in the function of multiple ecosystems at different grazing intensities. The study investigated EMF of mountain meadow grasslands on the northern slopes of the Tianshan Mountains in China, by way of a plant community survey coupled with high-throughput sequencing technology. The study calculated the EMF using the mean value method and explore the effects of no grazing (CK), light grazing (LG), and heavy grazing (HG) on grassland EMF. Results showed that HG significantly improved moisture regulation (MR) function (p < 0.05), and decreased soil fertility (SF) (p > 0.05), soil carbon storage (SCS) (p > 0.05), nutrient conversion and cycling (NC) (p > 0.05), grassland productivity (GP) function (p < 0.05), and EMF (p < 0.05). The EMF index of the grassland ecosystem under grazing conditions ranged from 0.3328–0.6018. GP, SCS, and NC functions had the highest contribution to EMF under CK, LG, and HG conditions, respectively. Under grazing conditions, EMF showed a cooperative relationship with SF, SCS, and GP, and the correlation coefficient (r) was between 0.62–0.76 (p < 0.05). At the same time, EMF and grassland water MR showed a relationship of trade-offs (r = 0.68, p < 0.05). The results of structural equation models showed that grazing had a significant effect on EMF directly, and also indirectly through soil fungal diversity. Therefore, reasonable reduction of grazing intensity is the most effective management approach for maintaining ecosystem function. At the same time, grazing plays a key role in maintaining EMF by regulating both above- and below-ground ecosystem functions, primarily through soil fungal diversity. This study elucidates the response of mountain grassland EMF to grazing intensity and provides a theoretical basis for restoring degraded grassland and sustainable ecosystem development.