Abstract: GMA was used exploringly as a coupling agent to improve the mechanical properties and durability of Wood Polymer Composites (WPC). The reaction mechanism and complex effect of interface between polymers and wood cell walls were analyzed before and after adding GMA into Styrene (St) with SEM and FTIR. The analysis results with SEM and FTIR indicate that GMA reacts with the hydroxyl groups of wood cell walls by it s epoxy group，and reacts with styrene as a free radical copolymerization form by its double bond，which makes the polymers graftfully on wood sell walls；and the polymers fill mainly in wood cell lumina as a solid form，which contact tightly with the wood cell walls. The testing results of comprehensive performance show that the modulus of rupture (MOR)，modulus of elasticity (MOE)，compression strength and hardness of WPC modified by GMA increase 45%，52%，71% and 141% compared with the unmodified WPC，respectively；the dimensional stability of modified WPC improves 3 times；and the decay resistance of the modified WPC increases by 8.56 times that of the unmodified WPC.