Abstract: The white-rot fungus Trametes sp.48424 was used to pretreat poplar heartwood for the biochemical-mechanical pulp(Bio-CMP). The laccase activity of white-rot fungus during pretreatment was measured, and the changes in the chemical composition of poplar heartwood before and after pretreatment were also analyzed. Moreover, scanning electron microscopy(SEM), Fourier transform infrared spectroscopy(FT-IR), carbon-13 nuclear magnetic resonance(¹³C NMR) were applied to intensively study the degradation mechanism of peplar heartwood by white-rot-fungus. Using Bio-CMP process, the changes of pulp fiber morphology and paper properties were discussed. The results showed that the white-rot fungus could perform solid-state fermentation well on the surface of the heartwood chips, and the laccase activity reached the maximum value of 1.3 IU/mL after 8 day of pretreatment. In the pretreatment stage, the white-rot fungus could lead to a porous and wrinkled surface structrue of the wood chip, and the degradation rate of Klason lignin was higher than that of holocellulose. White-rot fungus pretreatment could cleave β-O-4 side chain(δ 60.6, 72.7) substructure in milled wood lignin(MWL) effectively, while it had little effect on aromatic rings, reflecting that the degradation of lignin by white-rot fungus mainly happened on the lignin side chain. Compared with reference experiment,after poplar heartwood chips being pretreated by white-rot fungus, the fiber length and kinking index of the pulp increased, the content of fines reduced, and the paper strength enhanced obviously.