This work investigates the proposed welding of stainless steels with no backing gas by using solid wire ER316L-Si and mixed gases (He+Ar+CO_2). The protection mechanism was also discussed from the view of arc physics and the alloy elements in the solid wire. The result shows that when the proportion of helium in the above-noted mixed gases excesses 45 percent, the mechanical properties and the intergranular corrosion tendency meet corresponding Chinese standards. Further, the alloy elements in the solid wire can react with oxygen during the period of high temperature boosted by helium arc; this result in the formation of a bed of thin slag, which can avoid the oxidation of the backing weld and eliminate the need of backing gas.