To explore the role of soil bacterial communities in mediating soil multifunctionality under green manure catch cropping, four winter green manure varieties, with the winter idle field as the control (CK), were used in a field experiment to evaluate the contributions of soil bacterial biomass, species richness, network complexity, and community composition to soil multifunctionality in dryland Ultisols. The results showed that catch cropping promoted soil multifunctionality, especially for the Raphanus sativus L. and Brassica napus L., which were 54.36% and 55.65% higher than those of CK, respectively. Moreover, this catch cropping-induced increase in bacteria species richness, network complexity, and dominant taxa abundance (Proteobacteria and Gemmatimonadota) were associated with higher soil multifunctionality. Importantly, the species richness of soil bacteria was the key driver of soil multifunctionality, with a stronger effect than soil bacterial network complexity and community composition. This study highlights the importance of catch cropping-induced increase in bacteria species richness for promoting soil multifunctionality.