<p>The pulp and paper industry faces growing challenges arising from fiber shortages and environmental concerns. High yield pulping technology has emerged as a key solution, but the high lignin content in high yield pulp (HYP) restricts its brightness, posing a significant challenge for the bleaching process. Although traditional strong alkaline hydrogen peroxide (H₂O₂) bleaching of HYP is effective, it results in fiber yield loss and the generation of anionic impurities, thereby bringing about additional environmental burdens. In contrast, weakly alkaline H₂O₂ bleaching is more environmentally friendly and preserves a high pulp yield, but it struggles to achieve the desired brightness due to the reduced reactivity of lignin. This work addresses these challenges by investigating the effect of xylanase-pectinase (XP) pretreatment combined with weakly alkaline H₂O₂ bleaching to improve both bleaching efficiency and environmental benefits in the bleaching of poplar chemi-thermomechanical pulp (CTMP). The kinetic analysis reveals that the XP pretreatment significantly enhanced the efficiency of weakly alkaline H₂O₂ bleaching, accelerating lignin removal and increasing pulp brightness. The XP pretreatment effectively reduced the electrical conductivity, cationic demand, and chemical oxygen demand of the bleaching effluent. The mechanism studies demonstrate that the XP pretreatment effectively cleaved lignin-carbohydrate complex linkages and degraded hemicelluloses side chains, significantly increasing the accessibility and reactivity of the residual lignin. The integration of XP pretreatment with weakly alkaline H₂O₂ bleaching can offer a sustainable and efficient process for poplar CTMP upgrading, simultaneously enhancing the bleaching efficiency and mitigating the environmental footprint.</p>