Abstract: Larger size microcracks were found in the buffering layer when ENiCrFe-7 nickel-based welding material is used as filler metal to weld Q345B steel. Adopting optical microscope, scanning electron microscope and energy spectrometer were used to analyse the distribution, morphology, and precipitation of cracks and compared results with the the area where no crack occurs. The results show that cracks are only distributed in the buffering layer which adjacent to the base material, and the dilution rate, Fe content, and number of Nb-rich precipitates in the crack occurrence area are higher than those in the area where no crack occurs; The crack is typical solidification crack and precipitation phases rich in Nb and S elements exist on the crack surface; The low melting point phase rich in Nb and S is the main cause of solidification cracking of buffering layer.