The Zhoukoudian stock in Beijing consists dominatly of quartz monzodioriteand granodiorite formed by intrusions of two episodes. A few types of enclavesoccur extensively in the pluton. In the Guandi metamorphic complex at the south-ern border of the stock, massive diortic rocks were sporadically exposed. It isbelieved that the Guandi dioritic rocks and the main instrusive mass were resultedfrom crystallization of magmas at the same period; and the main rocks andenclaves in the pluton were produced by repeated mixing of possible three typeof magmas. Among them, amphibolitic enclaves are suppossed to be the result ofcrystallization reequilibrium of monzogabbroic magma. The surmicaceous enclavesare refractory residues from granodioritic magmatic souced. The finegrained quartzmonzonitic enclaves could be by derived by simple mixing of monzogabbroic andgranodioritic magmas; the microgranular dioritic enclaves are the possible productof the mixing of monzogabbroic, dioritic and granodioritic mgmas. Compositional variation of the host body is explained in terms of mingling of monzogabbroicand granodioritic magmas in different proportions as well as the Soret effect afteremplacement.