With sustainable development, wood is functionalized for use in energy-efficient buildings, lightweight vehicles, and water treatment applications. However, complex chemical or physical treatments hinder its practical application. Here, we propose a simple and efficient surface activation that uses UV-assisted hydrogen peroxide (H2O2) treatment for photoassisted oxidation in multifunctional wood manufacturing. The oxidized wood cell walls increase the number of hydroxyl groups on lignin. Combined with the aligned cellulose nanofibers, this creates strong capillary forces that enable automatic impregnation of functional precursors for nanomodification. The ammonium polyphosphate-activated wood shows enhanced fire resistance and mold prevention, with a 39% lower average heat release rate, a 1.71-fold longer ignition time, and complete resistance against typical mold species. Techno-economic analysis reveals that the preparation of surface-activated functional wood reduces 92.5% in energy, 76.8% in reagent cost, and a 169.1% increase in the market profitability than traditional impregnation. Life cycle assessment indicates that the surface activation strategy has 43% lower carbon emissions than vacuum-pressure impregnation. The surface activation is adaptable for both fluorophore nanomodification and graphite impregnation, endowing fluorescence and photothermal conversion to wood. This low-cost, efficient, and customizable surface activation approach represents a significant advance in the low-carbon manufacturing of multifunctional wood materials.