Abstract: Flocculation experiments on the effect of turbulent shear was conducted on the cohesive sediment collected in Huanghuacheng section of Zhongxian County along Three Gorges Reservoir. The experimental instruments included cylindrical settling column, flocculation separation chamber, and image collecting system. An approximately uniform turbulence flow was generated using oscillating grids in the cylindrical settling column, and the relation between the shear rate and the frequency of oscillating grids was calibrated using an ADV (Acoustic Doppler Velocimetry). The results showed that:① The apparent flocculation of cohesive sediment was observed, with the largest floc size D_f,95 ranging 73-126 μm and the mean size D_f,50ranging 18-33 μm, which were both strongly affected by the turbulent shear rate and the sediment concentration. ② D_f,95demonstrated a trend of increase followed by decrease with the turbulent shear rate (from 3.84 s^-1 to 30.07 s^-1), with its peak occurring at the shear rate 19.94 s^-1, when the percentage of large floc (larger than 96 μm in diameter) also reached the vertex. ③ Floc size distribution corresponding to different concentrations (0.3~1.0 g/L) at the same shear rate basically followed a tendency of D_f,95 increases with the sediment concentration.