In this paper, 18Ni300 samples were prepared by laser melting (SLM) technology. The heat treatment was studied by different heat treatment processes and cooling methods. The mechanical properties of the materials after different heat treatment were obtained by tensile test, Rockwell hardness and metallographic examination. Among them, 550 samples were annealed by stress-free annealing. After heat treatment at 820 + ageing 490, the metallographic structure is fine plate martensite with hardness up to 54HRC and tensile strength up to 1800 MPa. It has good comprehensive mechanical properties. This paper can provide reference for heat treatment of SLM printed metal parts.