Selective laser melting (SLM) of metal materials often results in irregular grains structures and high thermal stress, issues that can be addressed through heat treatment to achieve a more uniform microstructure and reduced residual stress. Therefore, the effects of three different heat treatment processes on the microstructure and mechanical properties of selective laser melting FeSiB/316L stainless steel were studied in this paper. It was found that after heat treatment at 400 ℃ for 2h, the internal grains were refined, resulting in an increase in dislocation density. Its tensile strength increases and the elongation did not change much. However, after heat treatment at 700 ℃ for 2 h, the grain size becomes larger, resulting in a decrease in dislocation density. The tensile strength decreased, but the elongation increased by 28% compared with the unheated FeSiB/316L composite sample. After heat treatment at 1 050 ℃ for 2 h, the structure of molten pool boundary and columnar crystal disappeared, which reduced the deformation resistance. The microhardness and tensile strength decreased by 42%, and the elongation increased by 2.5 times.