The invention discloses an antibacterial PCL (Polycaprolactone) plant fiber composite wire for 3D (Three Dimensional) printing and a preparation method thereof. The antibacterial PCL plant fiber composite wire is prepared from the following raw materials in parts by weight: 60 to 95 parts of PCL raw material, 1 to 20 parts of plant fibers, 1 to 15 parts of nano-filler, 0.1 to 3 parts of chain expanding agent and 0.2 to 2 parts of antibacterial agent. According to the antibacterial plant fiber composite wire disclosed by the invention, a renewable plant fiber resource and the antibacterial agent are added into a biological material polyepsilon-caprolactone (PCL) which can be completely degraded to prepare the composite wire; compared with a traditional PCL wire, the printing temperature ofthe wire is not changed; however, a printed product has good tensile strength, modulus and flexibility; meanwhile, the wire has relatively good antibacterial performance; a printing process of the product is smooth and a spraying nozzle of a printing machine is not blocked; the antibacterial PCL plant fiber composite wire is applicable to various 3D molding technologies; the printed product has anatural texture of woods and has a wide application prospect in the field of the 3D printing.