<p>This study aimed to evaluate the effects of cellulase or <i>Lactobacillus plantarum</i> (<i>L. plantarum</i>) on the fermentation characteristics and microbial community structure of the sorghum straw silage. Sorghum straw was treated with the following four experimental conditions: distilled water (control, CK), cellulase (CEL), <i>Lactobacillus plantarum</i> (LP), and a combined treatment of <i>Lactobacillus plantarum</i> with cellulase (LPCEL). These results indicated that the LP treatment could markedly (<i>p</i> &lt; 0.05) preserve the crude protein content compared to that in other treatments, whereas the CEL significantly (<i>p</i> &lt; 0.05) reduced the acid detergent fiber content, while the LPCEL had the highest lactic acid content and lowest pH value. Proteobacteria and <i>Pantoea</i> were identified as the dominant phylum and genus in fresh materials, respectively. This phylum level dominance transitioned to Firmicutes post-treatment, while at the genus level, the community shifted from <i>Pantoea</i> to co-dominance of <i>Lactobacillus</i> and <i>Prevotella</i>, with <i>Lactobacillus</i> being the most abundant in both the CEL and LPCEL treatments. In conclusion, adding <i>L. plantarum</i> and cellulase to sorghum straw can significantly improve the fermentation quality of sorghum straw silage, and improve the nutritional value of silage by affecting the microbial community structure and metabolic pathways.</p> Graphical Abstract <p></p>