The printing process parameters of Mar-M509 alloy formed by selective laser melting (SLM) are optimized. The optimized process parameters with less pores and microcracks are obtained. Two heat treatment systems of solution and solution + aging were designed to study the effects of heat treatment on microstructure and mechanical properties. Compared with as-built samples, heat treatment mainly leads to the production of two precipitates: bright white nearly circular Cr-Co rich carbide particles and dark gray long strip Ta-W rich carbide. The tensile test results at room temperature show that the as-built samples have a high tensile strength and yield strength. After solution treatment, the tensile strength of the sample decreases by 500MPa, while the tensile strength of the sample after solution + aging treatment decreases by about 350MPa. The main causes of strength reduction are grain coarsening and residual stress elimination during heat treatment. After solution treatment, the main precipitates are Cr-Co rich carbides with a small amount of large-size Ta-W carbides precipitate along the grain boundary. After solution + aging treatment, the content of Ta-W carbide increases and exists along grain boundary and in grain. The plasticity of the Mar-M509 superalloy has not been improved after heat treatment. Both heat treatments lead to a large number of carbides precipitated along the grain boundary, which is speculated to have an adverse effect on the plasticity. In order to improve the strength and plasticity of SLM Mar-M509 superalloy, the size and distribution of precipitated carbides need to be further regulated by heat treatment.