The IN718 alloys were fabricated by selective laser melting forming technique. The formation mechanism of solidi-fication structure and the behavior of phase transformation during heat treatment were investigated. The tensile fracture mechanism of IN718 alloy at room and high temperature after heat treatment was analyzed. The results show that the microstructure of sample is dendrite along building direction. Nanoscale Laves phase is distributed among the dendrites. The grain morphology has no obvious change after standard heat treatment. A large number of γ′

γ′′ and acicular δ phase dispersive precipitate. The content of Laves phase decreases and the hardness is about 40% higher than as-deposited samples. After heat treatment

the tensile strength of samples perpendicular to the building direction is higher than forgings. The plasticity of samples parallel to the building direction is better than forgings. The tensile strength is comparable to forgings at high temperature. The fracture mechanism of selective laser melted IN718 alloy after heat treatment is a through-granular ductile fracture mode of micropore aggregation.