Abstract: The evolution of microstructure and the initiation and propagation mechanism of microcracks during the tensile process of ERNiCrFe-13 welding wire deposited metal. The microstructure and fracture behavior of deposited metal were studied by in-situ tensile scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the microstructure of ERNiCrFe-13 welding wire deposited metal is mainly composed of columnar dendrite γ phase (NiCrFe solid solution), Nb and Mo rich in Laves phase (Cr,Fe,Ni)₂(Ti,Mo), MC carbides and eutectic structure in the interdendritic. The formation of Laves phase is mainly related to the segregation of Nb and Mo elements during solidification and has a size effect. Horizontal Laves phase size larger than 4 μm is prone to cracking. The fracture mechanism is the initiation of microcracks in the interdendrite precipitated phase under shear stress. Under the action of axial tensile stress, the connection is further extended along grain boundaries to fracture failure. The fracture is ductile and carbide segregation (NbC, TiC) and large Laves phase are the main causes of grain boundary cracks.