Recently, the realization of the combination of selective laser melting (SLM) and high-strength aluminium alloys (Al alloys) has been discussed in mainly the aerospace industry. However, there have been several problems for the realization, and the one of serious problems is the occurrence of micro cracks in high-strength Al alloy objects. To solve the problem, we focused on the addition of Si element to high-strength Al alloy objects to improve their fabrication properties. In this study, the effects of the addition of Si element on the fabrication properties and the mechanical properties of 7075 Al alloy objects in SLM were investigated. Our result suggests that the addition of Si element inhibited the formation of cracks in the SLM 7075 Al alloy objects, and the high density and crack-free Si added SLM 7075 alloy objects had higher mechanical properties than the case of a conventional Al alloy: AlSi10Mg.