The selective laser melting (SLM) is an advanced rapid prototyping technology developed in recent decades by using high energy laser beam to melt metal powder layer by layer. At present, the research on aluminum alloy by SLM at home is mainly concentrated on the Al-Si powder, and the research on the 7 series ultra-high strength aluminum alloy by SLM is still in the initial stage. A series of experiments were carried out on 7075 aluminum alloy powder for the SLM forming process. The microstructure properties and cracks of the 7075 aluminum alloy by SLM samples were analyzed by means of metallographic microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and other instruments. The results show that the crack in the sample is caused by component segregation, second T phase and η′(MgZn2) phase non-equilibrium phase precipitate because of component segregation. And with the increase of the laser energy density, the columnar crystal length, the depth of the molten pool, the mean length of the crack and the tensile strength of the sample increase, the number of cracks decreases.