The invention provides an automatic material changing device of a 3D printer. The automatic material changing device of the 3D printer comprises a support. The support is provided with a feeding pipe. The feeding pipe is provided with a feeding drive device. The support is connected with a rotating disk through a rotating shaft. The rotating shaft is provided with a rotating disk drive stepping motor. The rotating disk is provided with a plurality of material guiding pipes. The material guiding pipes penetrate through the rotating disk from top to bottom along the circumference of the rotating disk to be fixed. The side walls of the material guiding pipes are provided with silk material detecting devices. Material rollers are arranged above the material guiding pipes. Each material roller is provided with a material roller drive motor. Silk materials are wound around the material rollers, and the head portions of the silk materials downward pass through the material guiding pipes and the feeding pipes correspondingly to enter a print sprayer. By the adoption of the automatic material changing device of the 3D printer, automatic material changing operation can be achieved, switching is automatically conducted when a mold in multiple colors is printed, manual guarding is not needed, the work efficiency is high, and the work burden of an operator is greatly lightened.