The invention discloses an agriculture and forestry residue-based photo-thermal converted material for water treatment, a preparation method and application thereof. The method comprises the following steps: by adopting the abundant agriculture and forestry residues in China as the raw materials, crushing and performing hot briquetting, and then carbonizing the surface or attaching the materials, such as graphene, carbon nano tube or other metal nanoparticles, to the surface, thereby forming a photo-thermal converted material with low upper layer heat conductivity coefficient, high photo-thermal conversion efficiency, excellent lower-layer water-absorbing property and double-layer structure. The compounding steps are simple, the reaction device is simple, the operation is convenient and the acquired material has high solar energy use ratio, is low in cost and can be used for multiple times, so that the problems of high cost, low amplifying degree, complex preparation technology, low photo-thermal conversion efficiency, and the like, of the present photo-thermal converted material for treating water by utilizing the solar energy can be solved, and the technical problems of environmental protection and safety can be considered.