As a result of rapid developments in additive manufacturing (AM) technology, such as 3D metal printers, it is now possible to manufacture highly complex shapes that were hitherto difficult to produce using conventional manufacturing technologies. And many studies have been conducted in order to investigate the mechanical properties of porous structures fabricated by metal 3D printing technology. These reports conclude that the mechanical properties vary depending on the melting conditions during fabrication and that the resulting properties are much lower than their theoretical values. Indeed, this fact has been identified as an important issue in AM technology. One of the reasons for this issue is that when heat is applied to a metal powder via a laser beam, any excessive heat melts unnecessary powder away from the desired location, resulting in geometrical imperfections. The degree of them that can occur during AM and these effect on mechanical properties are still not fully understood. In this paper, the effect of geometrical imperfections on the compressive response of SUS630 lattice blocks fabricated by the selective laser sintering (SLS) technique have been investigated using FE simulation techniques. Here, geometrical imperfections were observed in a lattice structure that was scanned using a 3D X-Ray microscope (XRM). Based on these observations, two types of geometrical imperfection (strut radius deviation and center-axis offset), due to excessive heat transfer and the melting of unnecessary metal powder during the fabrication process were observed. Using this information, the effect of the amount of these imperfections on the mechanical properties of the lattice blocks was investigated. By introducing imperfections to the FE model, a likelihood of reduced mechanical properties can be potentially adverted. The main motivation of this study is to clarify the main factors that contribute to the reduction in mechanical properties. In addition, by comparing the amount of geometrical imperfections, the initial stiffness and plastic collapse strength in the models based on different strut diameters, we proposed appropriate manufacturing conditions for the lattice blocks that would minimize the reduction of their mechanical properties.