Al-13Si alloy with different addition amount of Sr were prepared and then poured into three kinds of moulds. Addition amount of strontium and solidification condition on microstructure of Al-13%Si alloy were discussed. It was found that solidification condition and addition amount of Sr were two main factors for modification efficient. The modification is better when the solidification velocity is faster as well as when Sr content is higher. The "post-modification" phenomenon is not found in this research. Remelting has little effect on the melting loss of Sr.