A low-cost process for removing boron from metallurgical grade silicon was developed by Si-Al alloying, and the separation procedure of silicon grains from Si-Al melt by solidification was investigated in this paper. The microstructure and purity of silicon were characterized and detected by metallographic analysis, energy dispersive X-ray spectrometers analysis and inductive coupled plasma atomic emission spectroscopy analysis. The results showed that the content of boron in the purified silicon decreased from 128.00 ppmw to 27.62 ppmw. In addition, the process of purification with Si-Al alloying combined with the treatment of hydrofluoric acid could remove boron to a low content of 13.81 ppmw, the removal rate of which is 89.21 %. The results indicated that the removal of boron from metallurgical grade silicon by Si-Al alloying is an efficient and prospective method.