Using the molten glass purification combined with the cycle superheating methods, a refined grain was achieved in undercooled Ni-Fe-Pb ternary alloy. The characteristics of microstructures and substructures of the high-undercooled refined grain were investigated by the transmission electron microscopy and the stress accumulation model. The grain refinement occurring at high undercooling was induced by the plastic deformation of dendrites and subsequent recrystallization, which was evidenced by high densities of substructures, e.g. dislocations, subgrains and migration of high angle grain boundaries.