Fine-grained sediment is commonly found in rivers, reservoirs, estuaries and offshore water bodies, and its flocculation and sedimentation is an integral part of mechanics of sediment transport. Here, experiments were conducted to monitor the flocculation and sedimentation process of cohesive fine-grained sediment with different concentrations of flocculants and sediment using a homemade experimental device, according to which the flocculation and sedimentation law of cohesive fine-grained sediment was analyzed and studied. The results show that among the flocculants, polyaluminum chloride (PAC) is relatively stable, and its optimal dosage does not change with the change of sediment concentration, which remains at 0.08 g/L. As for cationic polyacrylamide (CPAM), it is the most sensitive to sediment concentration, and the optimal dosage concentration of the flocculant can be divided into three stable stages and two sensitive stages with the change of sediment concentration; the optimal dosage concentrations corresponding to different sediment concentrations are 0.08, 0.10 and 0.12 g/L at the stable stages, respectively, and those at the sensitive stages can be selected using interval interpolation. In regards to anionic polyacrylamide (APAM), its optimal dosage concentration can be divided into two stable stages with the change of sediment concentration, and the optimal dosage concentration does not change with the change of sediment concentration during the stable stages, which is 0.08 and 0.10 g/L, respectively. In addtion, the optimal dosage concentration of APAM at the sensitive stage can be selected by interval interpolation as well. APAM has the best flocculation effect, followed by CPAM , whereas PAC performs poorly.