Reseeding diverse plant communities is a promising strategy for enhancing multiple ecosystem services, grounded in the fundamental assumption that greater biodiversity promotes higher levels of ecosystem functioning. However, current grassland restoration efforts often prioritize a single ecosystem service, which may enhance a limited number of ecosystem services at the cost of others. As a result, there is a lack of compelling evidence illustrating how vegetation reestablishment through reseeding positively impacts grassland ecosystem multifunctionality. To address this gap, we conducted a two-year field reseeding experiment in a degraded semiarid grassland in Northern China, aiming to assess how different levels of plant diversity influence the restoration of multiple grassland ecosystem functions. Our experiment established a plant species richness gradient (1-4 species), with legume forage included in every planting combination and all possible species mixtures fully covered. The results showed that increased species richness, combined with a balanced legume-grass composition significantly enhanced grassland ecosystem multifunctionality. Such positive association was closely related to improved soil functions, which act as a key linkage connecting plant diversity to overall ecosystem service supply. Our findings highlight the importance of adopting a multifunctionality perspective when evaluating the capacity of degraded grasslands to sustain multiple functions and services simultaneously, and provide practical implications for optimizing reseeding strategies in semi-arid degraded grasslands. This study offers a valuable reference for restoration ecology research, particularly as an early-stage assessment that warrants longer-term follow-up monitoring.