<p>Additive manufacturing (AM) technology is transforming the development paradigm of the manufacturing industry; a comprehensive understanding of the strength properties of additively manufactured metals is crucial for their application. This study utilizes the small punch test (SPT) combined with SEM and EBSD techniques to investigate the effects of printing power and heat treatment on the anisotropy of the mechanical properties, microstructures, and failure modes for selective laser melting (SLM)− 316L. The SPT curve and mechanical properties reveal that the anisotropy of SLM-316L is closely related to printing power and heat treatment, and the printing power has a greater impact. The relative anisotropy indicators are proposed to quantitatively analyze anisotropy, and those of strength are commonly contrast to those of ductility. The microstructure anisotropy of grain shape, grain size, and grain structure causes the mechanical anisotropy. Excessively high printing power causes the inner microstructure defects and leads to the great changing of anisotropy, and the homogenization heat treatment weakens the mechanical property anisotropy. Moreover, the anisotropy in the fracture mechanism is also observed, but the effect of printing power has the more obvious impact on the fracture mechanism. At last, the relationship among microstructure–mechanical property–failure mode is revealed to enhance the understanding of the anisotropy in the mechanical properties and failure modes for SLM-316L and provide valuable insights for its engineering applications.</p>