This paper is a comprehensive diseussion based on field observations and laboratory studies of metamorphic rocks and minerals in the Miyun Group. The mineral assemblages of the major rock groups (ultramafic, mafic and felsic metamorphic rock gsoups)and their evolution have been studied and the equilibrium among coexisting minerals in each metamorphic episode has been determined. On this basis, ACF and A'KF diagrams for two progxade zones of the first metamorphic episode and a µNaZO-µK2O diagram of the second me- tamorphic and inigmatitic, episode are produced. According to the results obtained, the metamorphism and the evolution of the mineral assemblages in the Miyun Group can be divided into three episo- des. The progressive metamorphism of the first episode belongs to granulite fades under intermediate pressure; the metamorphism and migmatization of the second,episode proceeded in an open system, with a general tendency of rising in µNa20 and dropping in temperature; and the third .regressive meta- morphic episode took place more later and superimposed heterogeneously on the previously , metamorphosed rocks. In the first two episodes,both mica and amphibole were stable. Orthopy- roxene was stable mainly in the Opx-Cpx none in the first episode, but in a few cases, it also occurs in some rocks with special composition in other zones. Glinopyroxene was stable in the first episode and the first stage of the second episode. Garnet appears only in the rocks with specific composition in the first episode, whereas in the second episode, but distributed widely in various rock types in the second episode.