6061 aluminum alloy is a kind of metal material widely used in aerospace equipment and automobile manufacturing, in the process of selective laser melting (SLM) forming, this material is prone to porosity and crack defects. Due to its poor printability, most current studies have not focused on its thermal dissipation value. This paper thoroughly investigated the effects of different forming processes and aging heat treatment on the densification degree, microstructure, and thermal conductivity of SLM-formed 6061 samples. The relationship of forming processes, defects, and thermal conductivity was revealed, and the influence mechanism of microstructure on thermal conductivity and its anisotropy was analyzed. The results show that the thermal conductivity of SLM-formed 6061 samples can exceed 140 W/(m·K), and the thermal conductivity can be further improved by about 5% – 30% after aging treatment. The thermal conductivity exhibits anisotropy, specifically showing higher thermal conductivity along the forming direction compared to the direction perpendicular to it, which is related to defects and grain morphology. This study provides a theoretical basis for the application of SLM technology in the preparation of high thermal performance aluminum alloy heat sinks.