Abstract: Inconel 718 alloy was prepared by laser powder bed fusion（LPBF）. The microstructure of Inconel 718 alloy was analyzed by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）. Crack initiation and propagation of Inconel 718 alloy were observed by scanning electron microscopy equipped with an in-situ tensile instrument.The results show that there are pores and inclusions defects in Inconel 718 alloy, and the microstructure is composed of cellular substructures. Nb and Ti elements segregate between the cells, and Laves phase and carbides exist between the cellular substructures. The original pores, inclusions and micro-cracks in the alloy are the main factors of crack initiation. The crack propagation modes in the alloy are transgranular and intergranular, and the crack preferentially propagates at the second phase. The fracture morphology of the alloy is composed of tearing edges, cleavage planes, dimples and a small amount of micropores, and the fracture mode is mixed fracture.