The surface of wood/polyethylene(PE) composites was treated by low pressure glow discharge of air plasma to improve its adhesion properties. To explore the failure mechanism in the condition of water for the bonding joint of wood/PE composites, the water resistance of plasma treated wood/PE composites bonding joint was studied and the effect of water on the surface properties of plasma treated wood/PE composites was investigated by using the analysis of contact angle, SEM and FT IR. The results show that the contact angle increases firstly and then decreases with the soaking time extended, the water absorption for the composite increases and the surface for the sample become more and more rough. However, the number of —OH, C—O and CO groups on the surface of plasma treated wood/PE composites decreases at first and then increases with the soaking time extended. And the failure mechanism in the condition of water for the bonding joint is related to the change on the surface roughness and chemical radicals for the surface of plasma treated wood/PE composites and the water absorption of the composites due to the soaking with water.