The invention relates to a 3D (3-Dimensional) printer based on fused-deposition rapid prototyping technology and a printing method thereof. The 3D printer and the printing method thereof are used for solving the problems that the existing 3D printers have the disadvantages of high printing cost, long printing time, high repair cost and the like due to the fact that printing heads of the existing 3D printers adopt a laser heating manner and the popularization of 3D print technologies is limited due to too-high use and maintenance costs. According to the printing method disclosed by the invention, the 3D printer comprises a heating workroom (1), wherein a wire feeding mechanism (2) is mounted at one side of the heating workroom, a working platform (3), two vertical Z axes (4) and two Y axes are mounted inside the heating workroom, the Z axes are connected with a servo motor A, an X axis (6) is connected between the Y axes, and a double-jet-nozzle print head (7) is mounted on the X axis; the wire feeding mechanism comprises two prototype material rollers (8), the prototype material rollers are provided with wire feeding devices (9), the wire feeding devices are connected with a servo motor B, and the servo motor A and the servo motor B are connected with an industrial personal computer; print jet nozzles (14) are mounted on the double-jet-nozzle print head. The printing method is applied to the 3D printer.