A metal 3D printing device comprises a building platform, a first powder spreading arm, a second powder spreading arm, a gas stream unit and a scanning module. The building platform is for supporting the powder. The first and second powder spreading arms are spaced and configured for spreading powder. The gas stream unites comprises a gas blowing port and a gas suction port, the gas blowing port is provided in the first powder spreading arm, and the gas suction port is provided in the second powder spreading arm. The scanning module is for emitting a laser to the powder preplaced between the first and second powder spreading arms to solidify the powder to form the product.