Abstract: Microstructure and chemical composition of the weld seam of K418 Ni-base superalloy prepared by laser welding were characterized by optical microscopy,scanning electron microscopy,energy dispersive spectrometer.And the weld cracking formation was analyzed.The results show that nailhead shape morphology of weld seam could form as the heat effect of plasma and metal vapor formed during the welding process.Microstructure of dendrites could be observed between weld seam and base metal.There were sawtooth and smoothness shapes at the interface of weld seam and base metal.Temperature range of solidifying was enlarged due to forming low melting point eutectics enriched in P,S and Si.Hot crack sensibility during the welding process was increased.