Abstract: Based on adding the cation high molecular weight polymer into the turbid suspended liquor containing 85 kg/m³ of sediments,this paper discusses the changing hydrodynamic turbulent conditions in the process of flocculation,such as shearing rate r (or velocity gradient G) and shearing time t,and the use of the settlement and the image analysis technology,the factor "fractal dimension D" which can characterize the fractal properties in quantity and the evolution regularities of the fractal structures of the bridging-flocculated aggregates.The results show that there are two critical values about hydrodynamic turbulent strength Gt (G₁t₁= 2350±100 at rapid flocculation stage and G₂t₂= 12400±100 at slow flocculation stage) when fractal structures reach the optimum state.It is found in experiment that the optimum Gt value is nearly the same when the compactness of the fractal structures of the bridging flocculated aggregates reaches the highest point of the different raw silt content.When raw silt content is low,r or G value should be reduced and t value increased However,the value of the fractal dimen sion D decreases Furthermore,when the fractal structures of flocs formed by the addition inorganic coagulant and the bridging-flocculation aggregates formed by the additional high molecular flocculant reach the optimum state with the same raw silt content,the former needs the higher Gt value,corresponding to the lower G value and the longer t value and the average mass fractal dimension D₃ value of floc is higher,but the fractal structure of floc appears frangible.