[Objective] To screen out a strain that can degrade lignocellulose for the application of lignocellulose deposited by delayed harvest of alfalfa under inappropriate climate and mechanical matching and provide strain resources for the efficient use of alfalfa. [Methods] The primary screening was carried out by culture with alkali lignin and sodium carboxymethyl cellulose. Based on color changes and fading circles, the strain with the ability to secrete ligninase and cellulase was screened out. The target strain was identified by 16S rRNA gene sequencing and whole genome sequencing, and then Kyoto encyclopedia of genes and genomes (KEGG) and carbohydrate-active enzymes (CAZy) were employed to annotate gene functions based on the whole genome sequence. The microstructure of the alfalfa stems degraded by the strain was observed by scanning electron microscopy. The nutrient and microbial community changes in alfalfa hay treated with the strain were evaluated. [Results] A strain S1 producing ligninase and cellulase was identified as Bacillus cereus by whole genome sequencing. A total of 305 genes involved in carbohydrate metabolism were annotated, including 139 genes encoding CAZy. After treatment with this strain, the microstructure of vascular bundles in alfalfa stems changed significantly. The crude protein content in alfalfa hay increased, while the lignin, neutral detergent fiber, and acid detergent fiber content and the alpha-diversity of microorganisms decreased over time. [Conclusion] The screened strain identified as B. cereus demonstrates a robust ability to degrade lignocellulose.