The microstructure and mechanical properties of 20Mn23AlV non-magnetic steel plate with thickness of 12 mm are compared by welding with different shielding gases.The results show that the appearance of weld surface of the test plate welded with 97.5% Ar+2.5% CO,2, shielding gas is better,and there are few pores in the weld.The welded joints with two kinds of shielding gases have good plasticity,toughness and tensile strength.The microstructure of the weld is white austenite matrix+δ ferrite. Using 97.5%Ar+2.5%CO,2, shielding gas is reasonable and can meet the non-magnetic steel welding production requirements.