The quartz monzonite-monzonitic granite masses are the main intrusive pro- ducts in Donghai area, northern Jiangsu and can be classified as I-type grani- toids, The major rock-forming minerals are composed of actinolitic hornblende, Mg-rich biotite, oligoclase, perthite and quartz, with sphene, apatite, zircon, mag- petite etc, as chief accessories. The thermodynamic calculation indicates that the physicochemical crystallization conditions of the magma are t=910一690℃, log fo2=-12, f H2o=(1.3-1.8) × 108Pa and log(fH2o/fHF)=3一4 , The 1 st set of transition elements are abundant in hornblende, biotite and sphene, but are obvi- ously reduced in oligoclase, perthite and quartz, As hornblende, biotite and oligo- clase play the most important part in the contribution of REE contents to the whole rocks, they control the REE distribution patterns of the rocks, These three minerals are usually rich in HREE with comparatively large negative Eu ano- maly, while plagioclase is relatively rich in LREE and exhibits positive Eu ano- maly, Thus, with the advance of magmatic fractionation, the mafic minerals and plagioclase will be gradually separated from each other, anal this will lead to the depletion of HREE, transition elements of 1st set and Eu contents.