Leymus chinensis (sheepgrass), a dominant perennial grass of the Eurasian Steppe, is a crucial source of carbohydrates and energy for ruminants. However, the lignocellulose recalcitrance severely limits its digestibility. Here, we targeted xylan, a major hemicellulose interacting with cellulose and lignin in cell wall. To improve digestibility, we knocked out two IRREGULAR XYLEM 14-LIKE (LcIRX14L) genes, which encode key enzymes for xylan biosynthesis. The Lcirx14L knockout mutants exhibited reduced xylan molecular weight but produced similar amounts of biomass to wild-type plants. Simon's staining and cellulase binding assays indicated enhanced cellulose accessibility in the Lcirx14L mutant. In addition, the Lcirx14L plant showed increased saccharification efficiency, dry matter and NDF digestibility, and production of volatile fatty acids by in vitro fermentation. This study thus provides novel insight for engineering forage grasses with both high yield and quality by modifying xylan polymerization.