•Gas protection improves the forming quality of deposited WE43-Mg by WAAM.•The cooling effect induced by gas protection enhances grain refinement.•Gas protection significantly reduces the content of oxides.•Eliminating oxide inclusions and refining grain enhances the mechanical properties. In this study, WE43 magnesium alloy was successfully fabricated using wire arc additive manufacturing technology, focusing on reducing the common oxide inclusion defects. The implementation of a gas shielding hood significantly improved the grain morphology of the deposited samples and diminished both the quantity and size of oxides. In addition, the cooling effect induced by the shielding gas contributed to the refinement of grain size. The synergistic effect of oxide reduction and grain refinement significantly improves the mechanical properties of the deposited samples. For heat treatable magnesium alloys, minimizing the consumption of rare earth elements is beneficial for optimizing heat treatment mechanical properties.