Leucocratic veins are widely distributed in the Fuping Complex, North China Craton, which demonstrates the intensive migmatization. The migmatization was generally ascribed to ichor metasomatism, pressure solution or fluid-absent partial melting, which are not consistent with the actual petrographic textures. Euhedral crystals of some minerals, albite-rim texture and typical transformation between hydrous minerals suggest that the migmatization has in fact experienced a complicated process which is characterized by water fluxed partial melting. The resultant melt was relatively mobile and can easily migrate into adjacent rocks. This is equivalent to injection of foreign melt into the rocks and resulted in melt-injection migmatization, causing some metasomatism reactions and textures. Therefore, metamorphic reaction of the Fuping Complex, resulting from migmatization, may include both melting or dissolution of feldspathic minerals and chemical transformation of one hydrous mineral (e.g., biotite) to another one (e.g., hornblende). The most crucial mechanism of migmatization of the Complex was dominated by water-fluxed melting or fluid-bearing partial melting, with pressure solution or fluid-absent anatexis as secondary factor.