Abstract: Microorganisms assisting with gut digestion of earthworm play a crucial role in degrading organic matter.Biochar can affect microbial populations by modifying substrate conditions, thereby influencing the vermicomposting process.However, the specific effects of biochar on gut microbes of earthworms remain poorly explored.In this study, the corncob biochar and rice husk biocharwere separately mixed into dewatered sludge with 5%（w/w） and allowed for a 7-day digestion period in the earthworm gut.The collected samples were pre-treated with propidium monoazide（PMA） to assess the number and community of active microbes.The results showed that biochar significantly enhanced the degradation and mineralization of organic matter, and nitrification in dewatered sludge（P＜0.05）.Compared to the control, the corncob biochar significantly increased the number of active bacteria and fungi in the earthworm gut by 4.04% and 25.03%,respectively（P＜0.05）.In addition, both biochars significantly elevated the Shannon and Chao1 indices of active bacteria in the gut（P＜0.05）,whereas, only corncob biochar significantly altered the β-diversity of the bacterial community.Moreover, both biochars promoted the abundance of Proteobacteria, with corncob biochar enriching nitrogen-cycling associated taxa.These findings indicate that biochar, particularly corncob biochar, enhances microbial abundance and alters microbial community structure in the earthworm gut.This study offers scientific evidence supporting the use of biochar to modulate the vermicomposting process and provides a theoretical framework for understanding the gut microbiota of earthworms.