Abstract: The cathode-heater assembly model for 3D printing was designed based on the technical characteristics of additive manufacturing. The samples in the diameters of 3 mm and 5 mm were 3D-printed by selective laser melting; meanwhile, the corresponding post-treatments for the samples were carried out, including the removal of support structure, the insulation protection of heater, and the impregnation of active material. The results show that, the cathode can be heated to the work temperature in range of 900~1100 ℃ by the new heater assembly, and the emission current density at the cathode inflexion can achieved as 7.94 A·cm^-2 at 1100 ℃ in water-cooled diode test.