Xylan, the predominant hemicellulose polysaccharide, serves as a crucial cross-linking polymer in cell walls and plays a significant role in modulating vascular function and the recalcitrance of lignocellulosic straw, thus affecting the digestibility of grasses. In this study, we identified a sweet sorghum mutant, designated M19, exhibiting softer leaves together with semi-dwarfism. Using MutMap+ analysis, we identified a loss-of-function mutation in the SbXyl gene, encoding an endo-1,4-β-xylanase of the glycoside hydrolase 10 (GH10) family, as the cause of the mutant phenotype. SbXyl is highly expressed in the developing internode and the truncated SbXYL protein in the M19 mutant results in altered cell wall morphology in vascular tissues. However, changes of cell wall components make the M19 mutant achieved a higher forage efficacy compared to the wild-type plant, as verified by in vitro rumen digestibility assays. Remarkably, vascular tissue-specific complementation rescued the growth defects of the M19 mutant while retaining its superior forage efficacy. Our findings open new avenues to improve grass straw quality for feed and contribute to the sustainable utilization of lignocellulose.