Dryland ecosystem stability is increasingly threatened by amplified precipitation variability, nitrogen (N) deposition, and grazing pressure. While these drivers independently alter grassland structure, their interactive effects on the critical diversity-productivity relationship remain poorly understood, particularly under contrasting precipitation regimes. Through a 3-year split-plot experiment (four grazing intensities & times; N addition) in a Loess Plateau steppe, we examined how interannual precipitation variability modulates the effects of grazing and N on the coupling strength between diversity (species richness, SR) and productivity (peak aboveground biomass, ANPP). Three key findings emerged: First, SR-ANPP coupling was strongly precipitation-dependent: low grazing with N enhanced their synergy in wet years, whereas drought combined with heavy grazing triggered severe decoupling. Second, functional group asynchrony drove these dynamics: ephemeral forbs amplified SR responses to wet years, whereas drought-tolerant grasses stabilized ANPP but accelerated SR collapse in dry years. Third, soil pathways mediated the coupling dynamics: precipitation and soil C-N pools facilitated coordination, while grazing-induced increases in bulk density exerted counteracting effects. Our CDS (Climate-Disturbance-Soil feedback) framework demonstrates that moderate grazing optimizes precipitation responsiveness when combined with strategic N inputs, offering actionable thresholds for maintaining coupled ecosystem functions under climate extremes. Plain Language Summary Grasslands cover vast areas of the Earth and provide essential ecosystem services such as food supply and carbon storage. However, their stability is increasingly threatened by more variable rainfall, nitrogen enrichment from the atmosphere, and livestock grazing. We examined how these drivers jointly influence the link between biodiversity (species richness) and productivity (aboveground biomass) using a 3-year field experiment nested within a 22-year grazing trial on China's Loess Plateau. We found that rainfall patterns fundamentally reshape this link: low grazing combined with nitrogen addition strengthens the coordination between diversity and productivity in wet years, whereas drought and heavy grazing disrupt it. These shifts arise because different plant groups respond asynchronously to rainfall-short-lived forbs dominate in wet years, while drought-tolerant perennial grasses sustain productivity in dry years. Soil processes also play a key role: richer soil carbon and nitrogen pools enhance coordination, but trampling-induced compaction weakens it. Our findings highlight practical strategies for sustainable management-maintaining low grazing with targeted nitrogen input in wet years and reducing grazing during droughts can help preserve resilient, productive grassland ecosystems under a changing climate.