The semi-solid AlSi7Mg alloy slurry with larger capacity was prepared by the compound technology of low superheat pouring and week traveling-wave electromagnetic stirring in this paper. The effects of electromagnetic stirring power and frequency on the shape and distribution of the primary α-Al grains of the semi-solid AlSi7Mg alloy slurry with larger capacity were discussed. The experimental results show that an ideal microstructure of the AlSi7Mg alloy slurry prepared by the compound technology of the low superheat pouring and week traveling-wave electromagnetic stirring can be obtained. When the pouring temperature is 630℃,the electromagnetic stirring power is 1.52 kW, the electromagnetic stirring frequency is 5 Hz, and the stirring time is 8 s ,the slurry with larger capacity, containing finer and more spherical primary α-Al grains distributed homogeneously can be obtained .At the condition of the low superheat pouring and week traveling-wave electromagnetic stirring, the pouring temperature is 630 ℃, the electromagnetic stirring frequency is 5 Hz, appropriately raising the stirring power can gain a better shape of the primary α-Al grains ,but if the stirring power is increased to a certain value（1.52 kw）, the shape of the primary α-Al grains can not be obviously improved and spherical primary α-Al grains distributed homogeneously can be obtained, the optimized processing parameter is 1.52 kW. At the condition of the low superheat pouring and week traveling-wave electromagnetic stirring, the pouring temperature is 630 ℃ and the electromagnetic stirring power is 1.27 KW, appropriately raising the electromagnetic stirring frequency can gain a better shape of the primary α-Al grains ,but if the electromagnetic stirring frequency is increased to a certain value（10 Hz）, the shape of the primary α-Al grains can not be obviously improved and spherical primary α-Al grains distributed homogeneously can be obtained.