The work aims to study the pore defects of Inconel 718 alloy fabricated by selective laser melting and scientifically classify the defects and explore the formation mechanism and then establish the corresponding relationship between the sputtering characteristics of the molten pool and the defect morphology to optimize the process parameters to inhibit the formation of defects. The microstructure and chemical composition of Inconel 718 powder were observed with scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. A digital video microscope was used to analyze the internal defects of the forming parts. The dynamic spatter process of metal droplets was filmed by high speed camera and the sputtering characteristic parameters were quantitatively analyzed. As the laser power increased, the energy density, the total number of sputtering drops and the number of pores al so increased. However, when the scanning speed increased, the energy density, the total sputtering area and the pore size decreased. Moreover, when the circularity of the defect was Circ≥0.731 or the aspect ratio of the defect was AR≤1.368, the defect morphology changed from irregular to regular. At the energy density E=95.24 J/mm3, the relative density reached 99.94%. The average values of porosity and pore size of all samples were 2.249% and 2.774 μm2, respectively. Pore defects can be divided into two types: irregular keyhole defects and regular stomatal defects. There are evolving circularity/aspect ratio thresholds. The sputtering characteristics change due to the shock of the molten pool, which corresponds to the defects with different morphologies. Decreasing the laser power and increasing the scanning speed can reduce the energy density and weaken the shock degree of the molten pool, thus inhibiting the formation of defects and increasing the relative density of the formed parts.