In this study, the influence of impurity elements Ca, P on the Sr modification treatment in Al-7wt%Si-0.3wt%Mg alloys was examined by the observation of microstructure, DSC analysis, tension test and fractographs. In the case of modification treatment by Sr 50ppm, the increase of Ca deteriorated eutectic modification rate and increased the primary and eutectic temperature. With the increase of Ca, ultimate tensile strength(UTS) and elongation were decreased and the fraction of intergranular fracture increased. The coexistence of Ca and P increased eutectic modification rate and depressed the eutectic temperature.