The efficiencies of chlorine dioxide delignification and oxygen delignification and corresponding bleaching sequences were investigated comparatively.The results indicated that the effect of ClO2 delignification (D0) on the modification of residual lignin was better than that of O2 delignification (O).Under the conditions of lower than and near to the removal rate of O2 delignification，the bleachability of D0 stage pulp was superior to that of O stage pulp.With the same removal percentage of delignification，the final brightness of bleached pulp by D0A/QP sequence and D0EP sequence were 11.2 and 10.3 points higher than the ones bleached by OA/QP sequence respectively，where A/Q stand for the acid chelating stage，E for alkaline extraction and P for hydrogen peroxide bleaching stage respectively.The CODCr loads of the D0 stage filtrate and corresponding mixed effluents by three stages of D0A/QP sequence were lower than those of O stage filtrate and corresponding mixed effluents by three stages of OA/QP sequence.Additionally，the characteristic absorption of aromatic ring of lignin was found in the UV spectroscopy of D0 filtrates and O filtrates.FT-IR spectroscopy analysis of unbleached and bleached pulps suggested that the amounts of hydroxyl and carbonyl increased in the D0 pulps and O pulps.With the subsequent bleaching stages，main chromophores such as carbonyl gradually decreased and a high brightness of pulp was obtained.The SEM analysis of fiber morphology revealed that the destruction and damage of the surface of fibers in D0 stage and corresponding D0A/QP sequence were less than those of O stage and corresponding OA/QP sequence.