Laser forming repair pre-tensile 7050 aluminum alloy with AlSi12 powder was studied using 300 W YAG laser. The optimized process parameters were obtained in multi-trace and multi-layer laser repair experiment. The elimination measures of metallurgical defects and the microstructures distribution of repaired zone were analyzed. It is found that the metallurgical defects including illbond, porosities and liquefied cracks can be eliminated through chemical treatment for the substrate surface, optimizing the process parameters and changing the powder condition. The microstructure at the bottom of the repaired zone is composed of the α-Al solid solution dendrite and a small number of Al-Si eutectic. With the increasing of the cladding layers, the eutectic volume fraction increases continuously, the α-Al solid solution dendrite is refined and the transformations from columnar grain to equiaxed grain take place. Finally, the completely refined equiaxed grains are achieved at the top of the repaired zone.