A novel biomass composite, wood-polymer composite with potential good mechanical properties, durability and environmental characteristic capable of applying in fields of construction and traffic as structural material, was prepared by generating high-performance polymer from in situ polymerization of styrene in wood porous structure. The vinyl monomer, styrene, combing with 1wt% AIBN as an initiation, was first impregnated into wood porous structure under a vacuum/pressure condition, and then in situ polymerized through a thermal treatment. The structure of the resultant composite was characterized by SEM, FTIR and XRD. Results show that styrene polymerized into polystyrene through free radical polymerization, and the resultant polymer fully filled in wood porous structure in a column form, partly contacting wood matrix. FTIR analysis indicates that polystyrene generated into wood pores, indicating weak interaction between them. XRD analysis suggests that the polystyrene generated into wood pores mainly existed in an amorphous form.