The Americal Old Corrugated Containers (AOCC) was treated with laccase. Fiber morphology, molecular weight and distribution of lignin were analyzed by scanning electron microscope (SEM) and gel permeation chromatography (GPC). Through the model compound of lignin (ferulic acid) was treated by laccase, the correlative mechanism for improvement of the wet-strength of pulp by laccase was discussed. The results showed that the molecular weight of lignin decreased and the lignin adhered on the fiber surface after the pulp was treated by laccase. While the laccase treated pulp with heating treatment, the condensation degree of lignin and adhesion area on fiber increased. In addition, when the ferulic acid was treated by laccase, the results were similar to AOCC pulp.