<p>Magnesium alloys hold significant potential for lightweight applications in aerospace, automotive, and other sectors, owing to their low density, high specific strength, and excellent processability. However, these alloys are prone to oxidation at elevated temperatures, exhibit high susceptibility to thermal cracking, and possess poor plastic forming capacity due to their hexagonal close-packed (HCP) crystal structure. These inherent characteristics impose stringent requirements on process control during additive manufacturing. In this study, single-pass multi-layer AZ31 magnesium alloy thin-walled parts were successfully fabricated via wire arc directed energy deposition (WA-DED) technology. The relationship between microstructure and mechanical properties at different deposition heights was systematically investigated. The results demonstrate that the microstructure of the thin-walled components, subjected to multiple thermal cycles, exhibits a layered distribution and consists entirely of equiaxed grains. All microstructures are composed of <i>α</i>-Mg, <i>η</i>-Al₈Mn₅, and <i>β</i>-Mg₁₇Al₁₂ phases. From the bottom to the top of the part, its tensile strength and elongation at break gradually decrease in the travelling direction. It is notable that there is no significant difference in mechanical properties between the travelling direction (TD) and the building direction (BD), indicating that it has excellent isotropic characteristics.</p>