Abstract: The investigation of effects of rare-earth yttrium and boron, which are in the 3.5% nickel-containing steel welding electrode on low temperature toughness has been carried out. The experimental results show that yttrium possesses an obvious action of deoxidization while the microelement boron can make crystal grains finer and can purify the filler metal, both can increase the low temperature toughness of weld metal markedly.