The invention relates to a method for separating and recycling a crystal phase from high-magnesium ferronickel slag, and belongs to the field of metallurgical slag comprehensive recovery and utilization. The method comprises the steps that ferronickel slag serves as a raw material and is subjected to magnesium enrichment treatment at first; a mixture composed of high-magnesium ferronickel slag andlow-magnesium ferronickel slag is obtained; the mixture composed of the high-magnesium ferronickel slag and the low-magnesium ferronickel slag is crushed to be 10-100 [mu]m; and magnetic separation is conducted, and the high-magnesium ferronickel slag is separated from the low-magnesium ferronickel slag, and during magnetic separation, the magnetic field intensity is controlled to be 7000-10000 gauss. The method is simple, easy to implement and low in cost, recycling of high-content magnesium oxide and silicon dioxide in the ferronickel slag is facilitated, it is possible for utilizing a large amount of ferronickel metallurgical slag, and considerable social and economic benefits are achieved.