Abstract: Different contents (0,10at%,20at%,30at%) of Sn were added into Si-Al alloy melt and then the alloy ingots were prepared. The effects of Sn addition on the dendrite width and recovery ratios of the primary silicon in the alloy ingots were studied. The results show that the dendrite width of the primary silicon increased with the increase of Sn content. When the silicon content was 31.86at%, the average dendrite width of the primary silicon increased from 490 μm to 710 μm with the Sn content increasing from 0 to 30at%. In the alloy ingot with a relatively low silicon content, the dendrite width of the primary silicon was larger and the increase effect of Sn addition on the dentrite width was more obvious. The recovery ratio of primary silicon increased with the increase of Sn content. When the Sn content increased from 0 to 30at%, the real recovery ratio increased from 62% to 85%.