A kind of environmental friendly novel composite flocculants which are used to treat raw water is prepared. It is made with chitosan (CS), iron modified polyaluminium chloride (CF-PAC) and modified montmorillonite on the principle of “the combination of organic and inorganic”. Under the optimum best compound formula and flocculation process, the turbidity of the waste water reduced by 0.62%, the chemical cost decreased by 12.43% and the content of aluminium ions dropped by 70.65%. There is an excellent characteristic and higher efficiency on the composite flocculant which can adsorb the organic matter in the water and chelate the heavy metal ions in the water.