Abstract: A 3-D printing method and a 3-D printout are provided. In an embodiment, the 3-D printing method includes laser-scanning a printing material according to a 3-D printing model so that the printing material starts to be sintered into a printout in a shape, layer by layer from the bottom up; and feeding a treatment gas into a 3-D printing device and laser-scan a local area of the printout so that the treatment gas reacts with the surface of the local area of the printout and a hardened layer is formed. The laser scanning and the feeding of the treatment gas are performed alternately until a printout with local hardened layers is formed. By adjusting the gas environment, the components can be manufactured by selective laser melting equipment to have a wear- and corrosion-resistant nitrided surface layer and keep the expected ductility of the central area.