Abstract: ASTRACT A 316L stainless steel/45# steel hybride material was fabricated by selective laser melting (SLM) 3D printing of gas atomized 316L stainless steel powder on a 45# steel substrate, and its microstructure and mechanical properties were investigated. The results showed that with the scanning speed (ν) of 1000 mm?s-1, laser power (P) of 225 W, powder bed thickness (d) of 30μm and scanning track spacing (h) of 100 μm, the SLM 316L stainless steel had the least defects, and was almost fully dense. With these process parameters, the SLM 316L stainless steel and 45# steel substrate achieved excellent metallurgical bonding, and the Charpy impact energy of the bonding region was 64 J. When the tensile loading direction was perpendicular to the bonding interface, the fracture occurred within the SLM 316L stainless steel rather than at the bonding interface, and the yield strength (YS), ultimate tensile strength (UTS) and elongation to fracture (EL) were 335.2 MPa, 619.9 MPa and 48.4% respectively, showing that the bonding interface had a higher strength than the SLM 316L stainless steel. The width of the heat affected zone across the bonding interface was about 120 μm, and contained a high number density of martensitic aciculae formed as a result of rapid quenching after solidification, and the microhardness of the bonding zone was obviously higher than that of the SLM 316L stainless steel and the 45# steel substrates. When the tensile loading direction was parallel to the bonding interface, the YS, UTS and EL of the hybrid material were 448.8 MPa, 653.2 MPa and 28.8% respectively.