Abstract: Three groups of Fe-Mn system flux-cored wires with different Mn/Ni mass ratios were designed for the stacking of thin-walled structural parts of non-magnetic steel by wire and arc additive manufacturing, and the three groups of specimens were tested by means of microstructural observation and performance testing. The results show that the microstructure of the three groups of specimens at room temperature is dominated by austenite, with a small amount of worm-like ferrite precipitated at the grain boundaries, and with the increase in Mn/Ni mass ratio, the austenite grains are refined and transformed from equiaxed to flattened at the same time. In addition, the ferrite grains also undergo a certain degree of refinement. With the increase in inclusions caused by the increasing Mn element, the inclusions are transformed from metal oxides to metal precipitates. With the increase in Mn/Ni mass ratio, the tensile strength, yield strength, and microhardness of the specimen increase, which is due to the combined effect of the reduction in the stacking fault energy and solid solution strengthening enhancement, but its plastic toughness has also been reduced. Calculations of the stacking fault energy of three groups of Fe-Mn system specimens with different Mn/Ni mass ratios show that the stacking fault energy of the specimens decreases with the increase in the Mn/Ni mass ratio. The permeability decreases as the Mn/Ni mass ratio increases, all of which satisfy the required range for non-magnetic steels.