Abstract: Selective laser melting (SLM) additive manufacturing technology can realize the rapid forming of magnesium alloy parts. However, comprehensive researches on mechanical properties and forming accuracy of magnesium alloy fabricated by SLM are limited. The densification behavior, microstructure, mechanical properties, surface roughness and dimensional accuracy of SLM-fabricated AZ91D magnesium alloy were investigated. The results show that the SLMfabricated samples achieve high relative density (> 99.5%) when the laser energy density for solid filling exceeds 110 J/mm³.However, there is no strict one-to-one correlation between relative density and laser energy density. The high relative density sample has fine dendritic microstructure and the ultimate tensile strength, yield strength and elongation all surpass those of the die-casting counterparts.The processing error of the high density and high performance sample is 0.25%when only employing solid filling strategy, but the surface roughness is as high as (17.7±1.9) μm. After introducing suitable contour scanning strategy, the surface roughness of the high density and high performance sample can be mitigated to (14.4±1.1) μm, accompanied by a reduction in processing error to 0.12%.