In order to improve the value-added applications of low-quality wood, a novel composite, wood-polymer composite, was fabricated by in-situ terpolymerization of MMA, VAc and St within wood porous structure. The structure of the composite and the reaction of monomers within wood were both analyzed by SEM and FTIR, and the mechanical properties were also evaluated. The SEM observation showed that the polymer mainly filled up wood pores, suggesting good polymerizating crafts. The FTIR results indicated that under the employed crafts, three monomers terpolymerized in wood porous structure, and grafted onto wood matrix through reaction of ester group from monomers and hydroxyl group from wood components, suggesting chemical combination between the two phases. The mechanical properties of the wood-polymer composite involving modulus of rupture, compressive strength, wearability and hardness were improved 69%, 68%, 36% and 210% over those of untreated wood, respectively. Such method seems to be an effective way to converting low-quality wood to high-quality wood.