The invention relates to a modified chitosan metal composition wood preservative and a preparation method, which is characterized in that,16 to 30 portions of bactericidal metal salt, 15 to 25 portions of chitosan, 6 to 18 portions of perboric acid and salts thereof and 250 to 300 portions of deionized water are mixed at 30 DEG C to 60 DEG C for reaction for 2 to 4 hours, wherein, the dried solid matter is white or green or grey powdery modified chitosan metal composition; then wood preservative aqueous solution is prepared by 0.5 to 5 portions of the metal composition, 0.5 to 2 portions of acid and 100 portions of water. The modified chitosan metal composition wood preservative prepared by the method has the advantages of high metal ion binding rate, broad-spectrum and high-efficient antiseptic effect and low viscosity; by using the preservative, the internal part of wood can be entered, and antisepsis, rot resistance and insect control treatment can be carried out to wood, bamboo and other plant fiber materials by soaking, brushing, spraying, pressure impregnating, etc.