Nanocrystalline materials are the most attractive materials in the field of materials science and engineering in the world. Nano-crystallization of metallic glasses is an effective way to prepare nanocrystalline materials. Here main nano-crystallization methods, including thermal crystallization, electrical crystallization, mechanical crystallization and crystallization under pressure etc. Their principle, problems associated as well as recent technological development are reviewed. The research progress in Tsinghua university in nano-crystallization of Bulk Metallic Glasses(BMG) treated by high density pulse current is simply reported.