Abstract: 18-8 stainless steel was welded using SJ612 flux, which was added with MnO of mass fractions of 0, 4%, 8%, 12%, 16%, 20%, respectively, and SAW-ER308 welding wire, and then the effects of MnO content on the microstructure, tensile property and corrosion resistance of the welded joint were studied. The results show that the microstructures in weld seams of all joints consisted of austenite and ferrite phases, and the ferrite content first increased then decreased with the increase of MnO content. With the MnO content increasing, the tensile strength and elongation of the joint first increased rapidly then slowly and tended to be stable when the mass fraction of MnO was over 12%; the corrosion resistance first increased then decreased. When the mass fraction of MnO was 12%, the corrosion rate of the joint reached the smallest value of 1.86×10^-5 g·mm^-2·h^-1, indicating that the corrosion resistance was excellent.