Al-7Si-0.3Mg based alloys have been widely used. Nevertheless, at least three issues during melt treatment (grain refinement of Al grains, modification of eutectic Si and refinement of eutectic grain size) need to be further explored. In this contribution, we focus on these three melt treatments. For grain refinement of Al grains, the stochiometric Al-2.2Ti-1B grain refiner rod together with 0.12 wt. % Ta was used. For modification of eutectic Si, Eu up to 500 ppm was used. The best modification can be obtained with 200 ppm Eu. By further increasing Eu up to 500 ppm, modification level becomes worse due to the formation of Al2Si2Eu. For the refinement of eutectic grain size, a combined addition of Eu (up to 500 ppm) and P (up to 40 ppm) was used. With increasing P concentration, the modification of eutectic Si became worse. The size of eutectic Si increases, the shape factor of eutectic Si decreases. When the P concentration is higher, more Eu is needed for a well-modified eutectic Si. This investigation provides a novel concept for melt treatment of Al-Si-Mg based alloys.