Studies on interfacial compatibility of wood plastic composites(WPCs) have received considerable attention in recent years. The effects on the surface modification by cellulase treatment and the mechanical properties of prepared WPCs were investigated in this study. X-ray diffraction(XRD) results show that the relative crystallinity(RC) of Hybrid Pennisetum(HP) could be significantly changed by the cellulase treatment. The RC of HP powders mainly goes through a phase that it first increases and then decreases by the treatment of cellulase. Five groups of different cellulase dosage and different treatment time were selected to do the mechanical and DMA tests. With proper dosage of cellulase and treatment time, the mechanical properties of WPCs could be improved. Finally, in the case of HP powder/cellulase of 4/1 and treatment time for 2 hours, WPCs show the best performance.