The chemical conditioners polymerized ferrous sulfate (PFS), poly(N-isopropyl-acrylamide) (PAM) and a self-made compound flocculant (S003) were used to investigate the dewatering effect on the actual polluted river sediments by simulating actual engineering conditions in the laboratory. The water content of dewatered cakes was 60.22% and 64.77% in the sediment conditioned with PFS and PAM, while the water content was 52.67% with S003. Compared with PFS and PAM, S003 achieved a faster settling rate and removed more turbidity. S003 achieved the best dewaterability of sediments because it had inorganic composition as sediments skeleton and organic compounds with bridging effect, contributing to form large dense flocs with porous structure, which speeded up the sediment settling rate and improved the filtration performance of sediments. In addition, the leaching rates of Cr, Cu, Zn, Ni, Pb and Cd in the solidified products were reduced by 55.8%, 92.1%, 89.2%, 61.4%, 34.2% and 56.3% respectively after conditioning with S003. It demonstrated that S003 greatly improved the sediment dewateribility and had excellent stabilizing effect on heavy metals.