Selective laser melting (SLM) Inconel718 alloys were heat treated at two different temperatures. The as-built samples, HT950 samples, and HT1050 samples were observed by light microscopy and scanning electron microscopy, and the hardness of these samples were tested. It was found that the microstructure of Inconel 718 alloy produced by SLM was squama-like. Columnar grains appeared after HT950 treatment, and the hardness was 80% higher than that of As-built sample. Equiaxed crystal and annealing twins appeared after HT1050 treatment, and the hardness increased by 44%.