This study aimed to identify types of lignin depolymerization products (LDP) and their role in humic substances (HS) formation, and little research has revealed which LDP could participate into HS formation during composting. Therefore, rice straw (RS), peanut straw (PS) and pine needles (PN) were selected for their different lignin structures to qualitatively and quantitative analyze LDP firstly. Qualitative results indicated that RS, PS and PN mainly produced LDP with G-type, common group and dimer structure. While quantitative results showed that RS and PS were more prone to degradation, and PN mainly promoted the formation of HS.During the lignin humification, Proteobacteria, Firmicutes, Actinobacteria-dominated microorganisms played a major role in facilitating monomeric substances into HS formation. This study comprehensively analyzed the process of depolymerization and humification of different kinds of lignin. It provides guidance for the resource utilization of lignin and the efficient treatment of agricultural organic waste.