Cellulase-poor xylanase was used to pretreat wheat straw pulp in order to study its reduction effects on the Cl2 consumption and its influence on the variation of lignocellulosic components during CEH bleaching process. The results indicated: After xylanase pretreatment, the Clz dosage could be decreased by 50% without affecting the targeted brightness. Xylanase pretreatment had removal effects on lignin of the pulp and could boost the dissolving of lignin during alkali extraction process. However, xylanase showed various degrees of depolymerization on pentosane and cellulose. The final lignin and pentosane content after bleaching of the enzyme-treated pulp were slightly lower than that of the control, whereas cellulose content was a little higher than that of the control.