Abstract The present study aimed to accelerate the humification and to investigate how MnO2 modification of biochar (MBC) drives the humus formation during composting with chicken manure. In this study, compared with the control group (CK), the addition of MBC caused an increase in the concentration of both humus and humic acid (HA), with a respective enhancement of 29.1% and 37.2%. In addition, MBC also improved the stability of compost products. Hetero two-dimensional correlation spectra further exhibited that the MBC could alter the formation mechanism of humus fractions during composting. Random forest analysis showed that Microbacterium, Bacteroides, Kroppenstedtia, Gracilibacillus, and Lentibacillus were significantly related to humus formation (P