Abstract: The development of cost-effective and environmentally friendly non-conventional water treatment technologies is urgent in response to the multiple challenges of global clean water shortage, sharp decline in fossil fuel reserves and increasing environmental pollution. Based on this, in this study, the gel reaction system was doped with biochar from rooibos straw treated under different calcination conditions as the photothermal component, and the gel polymer composites with excellent photothermal performance were prepared in one step at room temperature by regulating the contents of biochar and polyethyleneimine, and the Janus super-impregnated wood-based photothermal distillation device was constructed by reciprocal coating with a wood block as the substrate. The photothermal conversion efficiency and evaporation performance of the device were systematically investigated, and the influence of different salt concentrations on its evaporation performance was deeply analyzed. Under the solar radiation intensity of 1 kW·m⁻², the evaporation rate of the wood-based photothermal distillation device for pure water was 2.65 kg·m⁻²·h⁻¹, and the photothermal conversion efficiency reached 96.27%. In addition, the device also shows good stability and cyclic evaporation performance in high salinity environment, and still maintains the evaporation rate of 2.35 kg·m⁻²·h⁻¹ and 2.1 kg·m⁻²·h⁻¹ in brackish water and the reactive dye dyeing waste liquid of roving yarn. In conclusion, the wood-based photothermal distillation device combines excellent photothermal conversion efficiency and efficient water evaporation performance, which provides a low-cost and low-energy new technology solution for unconventional water treatment.