AbstractPrecipitation fluctuations strongly influence biomass production and its stability of terrestrial ecosystems. However, our understanding of the extent to which plant communities adjust their water‐use strategies in response to non‐growing season precipitation variations remains limited. Our 5‐year snow manipulation experiment in a semi‐arid grassland, complemented with paired stable isotope measurements of δ18O and δ13C for all species within the community, demonstrated that the impact of snowmelt on plant physiological activities extended into the peak growing season. Deepened snow enhanced ecosystem water use efficiency (WUE), biomass production, and its temporal stability. We further examined whether the observed increase in biomass stability was associated with the functional diversity of plant water‐use strategies. Plant cellulose Δ18Ocell analysis revealed that both community‐weighted mean and functional dispersion of stomatal conductance were positively associated with biomass production and its stability. The δ13C results further indicated that even with increased stomatal conductance, grasses were able to maintain their high intrinsic WUE by increasing photosynthesis more than transpiration. This resulted in higher biomass and greater dominance of high‐WUE functional groups under deepened snow. In addition, we also found that deepened snow increased root biomass, particularly in the 0‐ to 5‐cm and 20‐ to 40‐cm soil layers. This increase in root biomass enhanced the uptake of snowmelt from both surface and deep soil layers, further contributing to community stability. Overall, our study demonstrates that plant communities can optimize water acquisition and utilization, thereby enhancing the stability of biomass production through coordinated changes in plant physiology, species reordering, and root distribution under altered snow regimes.