The invention discloses a photocatalytic antibacterial biomass wood-plastic composite material and a preparation method thereof. The photocatalytic antibacterial biomass wood-plastic composite material mainly comprises the following constituents in parts by weight: 25 to 75 parts of thermoplastic plastic, 15 to 75 parts of wood powder, 5 to 20 parts of an inorganic filler, 1 to 10 parts of a modified nano TiO2 carried Ag+ and Cu2+ complex antimicrobial agent, 1 to 5 parts of a fire retardant, 1 to 10 parts of a lubricating agent, and 1 to 8 parts of a coupling agent. The composite material takes the modified nano TiO2 carried Ag+ and Cu2+ complex antimicrobial agent, the (waste) thermoplastic plastic, the (waste) wood powder and other auxiliaries as raw materials, so that the harm of mildew and rot and fungal infection of the wood-plastic composite material and termite and other insects is avoided, the environment is protected, and the resource waste is reduced. Taking the modified nano TiO2 carried Ag+ and Cu2+ complex antimicrobial agent as powder, the composite material has the characteristics that antibacterial and bactericidal effect is rapid and efficient, the composite material is safe and nontoxic, does not produce drug-resistance bacteria, is thorough, durable and stable, and has broad-spectrum antibacterial property, and the like, and further has the characteristics of double long effectiveness of photocatalytic antibacterial and antifungal effect of TiO2 and antibacterial and bactericidal effect of Ag+ and Cu2+.