The effects of trace yttrium (yttrium content 0.025%, 0.05%, 0.075%, 0.1% respectively) and T6 treatment on the microstructure and properties, on the eutectic transformation temperature of Al-7Si-0.3Mg alloy were studied by tensile test, hardness test, microstructure analysis of OM, SEM (+EDS), XRD and DSC. The tensile test and hardness test showed that the YS, UTS and E1% of the aluminum alloy after yttrium microalloying were improved, and the comprehensive performance with 0.05%Y was the best among the designed aluminum alloys. The microstructure and composition analysis showed that the strengthening phases were mainly Si and Mg2Si phase, and Mg2Si phase usually appeared with Si phase. DSC analysis showed that the added yttrium decreased the transformation temperature of α_Al+β_Si→Liquid, and it decreased 1.1℃, 2.0℃, 1.4℃ and 2.2℃ respectively when 0.025%, 0.05%, 0.075% and 0.1% Y was added respectively. In addition, the transformation temperature of α_Al→Liquid was increased somewhat after Yttrium microalloyed. An appropriate amount of yttrium that formed multiple phases with βSi, Mg2Si and so on, which promoted the formation of heterogeneous nucleation substrate, and improved the supercooling in solidification.