The invention discloses a 3D printing shoe-last forming method. The 3D printing shoe-last forming method comprises the steps that 1, a required shoe-tree model is downloaded, and a data format is modified; 2, shoe-tree data is output to a 3D printer, and a required shoe tree is printed; 3, an insole with the corresponding size and a heat insulating film with the corresponding size are selected, the shoe tree is sleeved with the heat insulating film, and the insole is nailed to the bottom of the shoe tree; 4, the shoe tree is sleeved with a shoe upper, the nails are used to fix the shoe upper to the shoe tree and the insole; 5, the shoe upper is repaired to be smooth through a hammer, then the insole and a lasting allowance of the shoe upper are bonded through glue, and then the nails are pulled out; and 6, a combining body of the shoe tree, the insole and the shoe upper is placed into a microwave oven for heating and sizing. According to the 3D printing shoe-last forming method, heating and sizing through the microwave oven can make the situation that a shoe last printed through a 3D printer can be manufactured into a shoe to be possible, and the heating and sizing time is greatlyreduced; and through the selective heating characteristic of the microwave oven, only the shoe upper is heated, and the shoe tree is not heated, so that swelling or melting of the shoe tree does not occur, and thus the sized upper part is more accurate.