Selective Laser Melting (SLM) technology has emerged as a pivotal additive manufacturing approach for aerospace-grade nickel-based superalloys due to its exceptional capability in fabricating high-performance complex components. However, inherent porosity defects – such as pores and lack-of-fusion (LOF) imperfections – present in SLM-produced parts significantly compromise their mechanical integrity, restricting their applicability in high-reliability engineering applications. Through a systematic investigation combining X-ray computed tomography (X-ray CT) imaging and high-temperature tensile testing, this study elucidates the critical role of processing parameters (laser power, scanning speed, and layer spacing) in governing porosity characteristics in GH4169 alloy. Notably, energy density (67 J/mm3) emerges as a threshold parameter dictating porosity morphology: sub-threshold energy inputs (<67 J/mm3) induce LOF defects (equivalent diameter > 30 μm, sphericity < 0.5), whereas supra-threshold regimes (>67 J/mm3) favor gas pore formation (equivalent diameter < 20 μm, sphericity > 0.8). Despite comparable porosity levels (<0.5%), specimens dominated by LOF exhibit a reduction of 15–20% in tensile strength relative to gas-porous counterparts, attributable to their irregular geometries and elevated stress-concentration factors. Optimization of processing parameters (laser power: 270–300 W, scanning speed: 860–1060 mm/s, layer spacing: 0.11–0.13 mm) enables porosity suppression below 0.15%, concurrent with attainment of 1,350 MPa tensile strength at 400 ℃—a 58% enhancement over conventional casting counterparts.