A new Al-4.77Mn-1.37Mg-0.67Sc-0.25Zr alloy (wt.%) was prepared by selective laser melting (SLM) technique under different processing parameters, and the microstructure and mechanical property of the SLM alloys were investigated by tensile tests and microscopy methods. The results show that when the energy density ranges from 104 to 143 J/mm³, the mechanical properties remain relatively stable. The yield strength, ultimate tensile strength and elongation are 335-338 MPa, 397-400 MPa and above 11%, respectively. Meanwhile, few defects and coarse intermetallics form and lots of fine AlFeMnScZr phases precipitate. When the energy density exceeds 152 J/mm³, some cavities and cracks can be observed, and elongation decreases sharply. The quantitative calculation results show that the solid solution strengthening, grain boundary strengthening and precipitation strengthening account for 44%, 41% and 15%, respectively.