Al-14.4Mg-0.33Sc-0.19Zr aluminium alloy with wide particle size distribution powders (2-46 μm) and high Mg-content was prepared by selective laser melting (SLM). The effects of different process parameters and aging treatment on the processability, microstructure and mechanical properties of SLM-formed Al-Mg-Sc-Zr alloy were systematically studied. Experimental results showed that the high laser power could effectively reduce the influence of fine powders splash on the processability of the samples. The maximum relative density of the sample reached 98.6%. The microstructures of the samples composed of fine equiaxed grains and coarse grains. The increase of Mg content in Al-Mg-Sc-Zr alloy reduced the texture and the content of columnar grains. The micro-hardness first increased and then decreased with the increases of aging temperatures. Both micro-hardness and compression yield strength showed dual-peak phenomenon with the increase of aging time at 350 ℃. The maximum micro-hardness ~ 163±3 HV and compressive yield strength ~ 457±10 MPa appeared for the sample ageing treatment at 350 ℃ for 1 h, with an elongation of 27±3%. After aged the samples at 350 ℃ for a long time, the micro-hardness and compressive yield strength of the sample decreased due to coarsening of the precipitated particles. In this study, the utilization ratio of the powders were efectively improved by increasing the particle size distribution of alloy powders, and SLM-formed high Mg-content Al-Mg-Sc-Zr alloy exhibited good processability and mechanical properties.