A series of composite flocculants polyaluminium chloride (PAC)-polydimethydiallyammonium chloride (PDMDAAC) was prepared by using PAC with different basicity (B) and PDMDAAC was raw materials. The electrical charge of PAC-PDMDAAC was studied by electrophoretic mobility method. And the flocculating efficiency of PAC-PDMDAAC on treating water from Yellow River was also preliminarily examined by Jar-test. The experimental results show that the PAC-PDMDAAC is characterized by giving higher positive Zeta potential value and better flocculating effect than PAC. The B value of PAC and the content (P) of PDMDAAC in PAC-PDMDAAC had some effect on the Zeta potential and the turbidity-removal efficiency.