Additive Manufacturing (AM) technology has advantages in building free shape and simplification of manufacturing process. In order to manufacture the high quality parts, it is important to find out the optimum fabrication parameters such as laser power, scan speed, scan pitch and so on. In this research, the fabrication conditions under high power and high scan speed were investigated to fabricate the sound parts of Al-10Si-0.4Mg alloy using a SLM machine equipped with a 1 kW single mode fiber laser. As a result, the effective process window in the process map of the laser power and the scan speed was found out by evaluating the density of the specimens. The range of the energy density that showed high relative density of the parts was 35~80 J/mm³, and it was similar to the result reported by other researches. In the case of the laser power of 700 W, it was found that the relative density keeps high value even at a scan speed of 2200 mm/s. Thus, it was found that the sound parts can be fabricated at high scan speed by increasing the laser power. And the optimum scan pitch was similar to the laser spot size.