Abstract: High lignocellulose content in tomato stalks hinders their resource utilization. To achieve rapid humification of tomato stalk lignocellulose, two treatments were established using tomato stalks as the primary material: Fine-crushedTomato Stalk (FC) and Coarse-crushed Tomato Stalk (CC). Changes in physicochemical properties, humic substance content, and bacterial community structure during composting were monitored to investigate the effects of different crushing degrees on lignocellulose degradation, humic substance formation, and bacterial communities. Results showed that the FC treatment significantly increased the maximum composting temperature (64.53 ℃) and prolonged the high-temperature period (7 days). At maturity, the total nitrogen (TN) content in the FC treatment (2.48%) was significantly higher than in the CC treatment (2.08%). Compared to CC, the FC treatment exhibited significantly reduced cellulose and hemicellulose contents (by 8.81% and 21.17%, respectively), increased humic substance (HS) content (by 22.15%), enhanced humification degree, and reduced NH₃ and N₂O emissions (by 28.18% and 24.86%, respectively). During the heating and thermophilic phases, the FC treatment showed higher relative abundances of lignocellulose-degrading and humification-promoting bacterial groups, including the phyla Actinobacteriota and Firmicutes, as well as the genera Paucibacter, Cerasibacillus, and Pseudogracilibacillus. Co-occurrence network analysis revealed higher modularity and tighter connections among bacterial communities in the FC treatment, indicating that fine crushing promotes substrate homogenization and drives the formation of specialized cooperative modules among functional bacteria. Mantel test analysis further demonstrated significant correlations between cellulose, hemicellulose, lignin contents and α-diversity, β-diversity, as well as core bacterial communities in the FC treatment, confirming that this modular division synchronously optimizes lignocellulose degradation efficiency and humic substance formation. In summary, fine crushing of tomato stalks accelerates lignocellulose degradation, enhances humic substance production, and optimizes microbial community structure, thereby effectively improving the quality and efficiency of tomato stalk composting and providing a scientific basis for efficient resource utilization of tomato stalks.