Solvent refining is one of the processing methods for production of solar-grade silicon. During Al-Si solvent refining process, the cooling rate has a significant effect on microstructure and purity of primary silicon. In this paper, the Al-30wt%Si melt was solidified at different cooling rates, then the microstructures and impurity contents were analyzed. The results show that the length and width of primary silicon increase with the cooling rate decrease, which results in the increase of recovery rate of primary silicon. The <111>-orientation was preferred in the lower cooling rate range during growth of primary silicon grains. Meanwhile, it is obvious that the impurity content is related to the cooling rate. In the lower cooling rate range, the removal rate of impurities is higher, especially for the B and Ti impurities. Accordingly, to improve the recovery rate and purity of primary Si in the refining process of Al-30wt%Si alloy, the cooling rate of molten solvent should be lower than 3 ℃/min.