A new kind of rare earth- containing flocculant of poly-ferric sulfate chloride (PFSCRE) was studied, and proved to produce high density floccules growing, make sludge deposit quickly and possess high COD removal rate, so that it is seen to be more effective for the disposal of dying wastewater than PFSC. The optimum process for preparing the PFSCRE is defined as REC/PFSC 1.2% ～ 2.2%. And each correlativity of configuration with capacity of aggregating sludge was respectively educed through analysis and comparison of configurations of them. Finally, a prediction was put forward that it should be the key for development of the PFSCRE agglomerating capacity to manage to increase its degree .of polymerization.