The invention relates to an anti-corrosion wood decoration system of an outer wall and a construction method thereof. The system comprises an anti-corrosion wood plate, pendants and a keel bracket connected to the outer wall, wherein the anti-corrosion wood plate is formed by splicing anti-corrosion wood strip plates into a panel in a side by side mode; the back of the panel is formed by longitudinally connecting the anti-corrosion wood strip plates into an integral plate through a back panel; the anti-corrosion wood strip plates and the back panel are fixed through screws; the upper and the lower ends of the back panel are respectively fixed with a connecting wood plate; the connecting wood plate arranged on the upper end is provided with pendant mounting slots with openings upwards; the connecting wood plate arranged on the lower end is provided with the pendant mounting slots with the openings downwards; the shapes of the pendant mounting slots of the upper and the lower adjacent anti-corrosion wood plates are in a long strip shape, and the positions are in an up and down correspondence; and the upper and the lower adjacent anti-corrosion wood plates are connected with a transverse keel through the pendants embedded into the pendant mounting slots. The invention has the advantages of short construction period, no influence from climate and environment factors, clean construction environment maintenance and construction cost reduction. The invention integrates functionality and decoration, and can be widely applied to the decoration construction of the outer wall of a building.