The invention discloses an Al-Mg-Sc-Zr series aluminum alloy composition for selective laser melting technology and a preparation method for a molding part. The composition comprises, by mass, 6-15% of Mg, 0.5-4% of Sc, 0.7-3% of Zr, 0.5-2% of Mn and the balance aluminum. An aluminum alloy molding part are prepared by smelting of master alloy, preparation of metal powder, preparation of aluminum alloy molding parts and heat treatment processes. According to the elective laser melting technology, the solubility of Mg, Sc and Zr alloy elements in aluminum matrix is greatly improved, the concentration of solid solution strengthening elements and dispersion strengthening particles in the aluminum alloy is increased, and the mechanical property of the aluminum alloy is improved. According to the aluminum alloy obtained by preparation of the selective laser melting technology, the highest density is 99.8%, the highest extension strength sigma b reaches 550 MPa, the yield strength sigma0.2 reaches 520 MPa, the plastic deformation rate of about 12 % is maintained, and the Al-Mg-Sc-Zr series aluminum alloy composition for the ctive laser melting technology and the preparation method for themolding part is applied to complicated structural parts with higher mechanical properties.