Abstract: In optmizing design and property tests of welding electrode E5018,influence of slag basicity,content of element Mn and Si as well as Mn/Si ratio in weld metal on low temperature impact toughness of the weld metal was investigated.The results indicate that when basicity is about 2.1,Mn content is 1.42%~1.48%,Si content is 0.38%~0.48% and Mn/Si>3.5,the low temperature impact toughness of the weld metal will be relatively high and stable.