Abstract: The metallurgical effect of light rare-earth on inclusion in weld metal has been investigated by means of scanning electron microscope,X-ray energy dispersion spectrometer,micropatical analyzer,electron probe microscope and thermodynamic analysis.The results showed that after light rare-earth alloys were transferred into the weld metal through coating electrode,they had the function of cleaning and modifying,morever their action of deoxidization was stronger than that of desulfuration.