Abstract: The betula alnoides wood powders are treated by xylanase solution. The betula alnoides/HDPE composites are prepared by hot-pressing forming technique. The effects of the solution reaction time, temperature and concentration on the tensile strength and the bending strength of the betula alnoides/HDPE composites are investigated. The optimum chemical reaction conditions of the betula alnoides wood powders in the xylanase solution are established. The transformation of chemical functional groups of the betula alnoides wood fibers are analyzed by FTIR and their morphologies of fracture surfaces are observed using SEM. The results show that the interfacial bonding in the betula alnoides/HDPE composites are enhanced after xylanase solution. After the wood fibers are treated in a xylanase solution of concentration 2.67 mg/L under the conditions of a temperature of 40℃ and a pH of 4.5 during 2 h, the relative content and crystallinity of cellulose and the relative content of lignin increase in the betula alnoides wood fibers, while the relative content of hemicellulose decrease. The comprehensive mechanical properties of the betula alnoides/HDPE composites are enhanced due to the increased interface area between plastic and treated wood fibers whose surface become softer and rougher.