Intensive grazing can threaten biodiversity and reduce the capacity of grassland ecosystems to sustain multiple ecological functions, particularly in arid regions. How grazing intensity shapes biodiversity, ecosystem multifunctionality, and their interrelationship remains poorly understood. Using a long-term grazing experiment in a desert steppe in northern China, we tested how grazing intensity (at four levels: no, light, moderate, and heavy grazing) affects above- and belowground biodiversity, ecosystem multifunctionality, and their relationship. We found that light grazing increased ecosystem multifunctionality, particularly aboveground multifunctionality. In contrast, moderate and heavy grazing reduced ecosystem multifunctionality, affecting both above- and belowground multifunctionality. For single ecosystem functions, light grazing enhanced productivity, whereas moderate and heavy grazing simultaneously suppressed productivity, carbon cycling, and nutrient supply functions. Notably, under no and light grazing conditions, ecosystem multifunctionality was primarily driven by aboveground diversity, with plant diversity playing a dominant role. In contrast, belowground diversity, especially soil bacterial diversity, became the primary driver of ecosystem multifunctionality under moderate and heavy grazing conditions. Therefore, our findings highlight that the strength and nature of the biodiversitymultifunctionality relationships are shaped by grazing intensity, and light grazing either enhanced or maintained high levels of both biodiversity and ecosystem functioning, offering a promising strategy for sustaining multifunctionality in the desert steppe.