The microstructure, hardness, precipitates and phase transformation are studied before and after a process of 1050°C solid solution + double ageing for Inconel 718 alloys fabricated by SLM. The test results show that the obvious weld beads structure can be observed on unheated surface of alloys. The microstructure shows seriously inhomogeneous with distributing columnar crystals and fine dendrites. After the heat treatment, the microstructure shows the homogeneous bulk crystal structure. The typical columnar crystals and dendrites also disappear. Some intermetallic compounds and segregated hardening phase, Ni-Cr-Co-Mo, FeNi and Ni8Nb, are dissolved. δ phases of solution were dispersed in grain interiors, which was gathered in grain boundaries with different size. The growth of grain that shows relatively fine structure is limited.