The invention discloses a 3D printing method adopting fused deposition molding. According to the method, a thermoplastic wire rod is conveyed to an extrusion head through a wire conveying mechanism, the wire rod is extruded by the extrusion head to form fuse wires in a semi-fused state, the materials are not directly molded after being extruded, the extruded fuse wires in the semi-fused state are stretched firstly to be thin, and then the fuse wires are subjected to deposition molding 3D printing in a molding chamber. By means of the 3D printing method, the material extrusion speed is increased, and therefore the deposition molding speed is increased, and 3D printing efficiency is improved; under the condition of the same precision, the manufacturing efficiency is improved by more than 4 times. The minimum width of the deposited fuse wires can reach 0.03 mm, and compared with the prior art, the minimum width is decreased by more than 3 times. The materials and devices adopted by the method are proximate to those of the prior art, the equipment cost and the material cost are equivalent to those of the prior art, and the using cost is lowered due to improvement of production efficiency.