TiB₂/18Ni300 composites with different mass fractions of TiB₂ were prepared by selective laser melting technique, and the effects of different mass fractions of TiB₂ on the surface morphology, microstructure, EDS spectra, XRD phase structure and mechanical properties of the specimens prepared were investigated. The results showed that with the increase of the TiB₂ mass fraction, top surface of the specimens roughened, the spheroidization effect was enhanced, and the surface porosity enlarged. Meanwhile, the cellular crystal-type solidified structure gradually changed to columnar crystals, in which Ti elements were uniformly distributed. The main crystalline phases of the specimens were α-Fe martensite, with a gradually increasingly intensified diffraction peak. Moreover, the Vickers hardness and tensile strength of the specimens showed a change trend of increasing at first and then decreasing, and the ductility gradually decreased. The specimen containing 0.5% TiB₂ had the greatest hardness and tensile strength, which were 409 HV and 1485.8 MPa, 15.78% and 53.1% higher than those of the 18Ni300 specimen without TiB₂ powder addition, respectively. Different from the plastic fracture of the 18Ni300 specimen, the fracture mode of the TiB₂/18Ni300 specimen was plastic and brittle fractures.