An object of the invention is to provide a method for producing a large amount of inexpensive high purity silicon useful for a solar battery. Disclosed is a method for producing high purity silicon by migrating impurities in silicon to slag including performing a first slag purification of a first silicon, separating the slag from the first silicon after finishing the first slag purification, and feeding the separated slag to a second molten silicon in a second purification of the second silicon, wherein purity of said second silicon prior to purification is lower than purity of the first silicon after purification.