Lignocellulosic degradation is a bottleneck of bioconversion during the composting process. In-situ generation of H 2 O 2 in the composting system was an ideal method for efficiently promoting lignocellulase degradation, and zero valent iron (ZVI) was concerned because it can generate H 2 O 2 by reducing dissolved oxygen. This study focused on the effects of ZVI treatment on lignocellulose degradation, microbial communities, and carbohydrate-active enzymes (CAZymes) genes during composting. Its results indicated that ZVI increased H 2 O 2 content during composting, accompanied by the formation of •OH. The degradation rates of lignin, cellulose and hemicellulose in ZVI group (20.77%, 30.35% and 44.7%) were significantly higher than in CK group (17.01%, 26.12% and 38.5%). Metagenomic analysis showed that ZVI induced microbial growth that favored lignocellulose degradation, which increased the abundance of Actinobacteria and Firmicutes but reduced Proteobacteria. At the genus level, the abundance of Thermomonospora, Streptomyces , and Bacillus significantly increased. In addition, glycoside hydrolases and auxiliary activities were important CAZymes families of lignocellulose degradation, and their abundance was higher in the ZVI group. Redundancy analysis showed that the increased H 2 O 2 and •OH content was a critical factor in improving lignocellulose degradation. Overall, H 2 O 2 as a co-substrate enhanced the enzymatic efficiency, •OH unspecifically attacked lignocellulose, and the increase in functional microbial abundance was the main reason for promoting lignocellulose degradation in composting. [Display omitted] • Contributions of H 2 O 2 produced by ZVI were identified in composting. • In-situ generation of H 2 O 2 promoted the degradation of lignocellulose. • The abundance of CAZymes induced by ZVI increased significantly. • A practical lignocellulosic biomass depolymerization strategy was proposed. [ABSTRACT FROM AUTHOR]