Aimed at the electromagnetic separation process of high silicon aluminum silicon alloy, addition of the modifier Sb in the separation process was proposed to and the effects of the addition amount of the modifier Sb, the pull-down rate, and the temperature on the separation effect in the electromagnetic separation process of the high silicon aluminum silicon alloy (45wt% Si) to strengthen the separation of primary silicon and alloy were studied. In the early stage of the directional solidification process, the modification experiment was carried out to perform XRF detection and FEI-SEM scanning of the silicon content in the primary silicon enrichment area of the sample, and the EPMA analysis of the micro morphology of the alloy part. Later, referred to the Sb modification mechanism in the relevant literature, Comsol software was used to simulate the electromagnetic directional solidification process of Al-45wt% Si. The separation theory of primary crystal silicon and the theory of silicon grain refinement were used to discuss the metamorphic behavior of Sb. After the addition of Sb, the eutectic reaction temperature of the aluminum-silicon alloy decreased and the entire solidification process became longer. Theoretically, the primary crystal silicon can obtain more sufficient growth conditions, which was beneficial to the enrichment of the primary crystal silicon. The results showed that after adding the modifier at 1500℃, when the pull-down rate was 10 μm/s, the silicon content in the silicon-rich phase increased from 86wt% to 90wt%. When the pull-down rate was 40 μm/s, the silicon content in the silicon-rich phase increased from 81wt% to 86.5wt%. At the same time, after adding the modifier, the eutectic silicon phase of the alloy was uniformly and continuously distributed in the α-Al matrix, and the morphology was refined.