Abstract: Plate and frame filter press dewatering technology has been gradually popularized and applied in dredging sludge treatment projects, but there are problems such as poor targeting of flocculant selection and unclear mechanism. In response to the phenomenon, two typical polymer flocculants are selected, one is the synthetic polyacrylamide flocculant with more applications in engineering, and the other is the natural environment-friendly flocculant chitosan. Through the measuring cylinder sedimentation column test, the study of anionic polyacrylamide (APAM), chitosan, these two flocculants in different dosage of silt sedimentation and dewatering rule of change, to get the optimal flocculant dosage, in the optimal dosage of silt sedimentation stabilization of the mud surface settlement amount compared to the original mud increased by 25.9%, 32.4%. On this basis, a combined flocculation and plate and frame filter press dewatering test was carried out, and the results showed that the addition of APAM had a greater impact on the dewatering of sludge in the filtration stage; the dewatering effect of the chitosan-added sludge was better in the filter press stage. In the process of plate and frame filtration, the water yield of the sludge cake with APAM and chitosan flocculants increased by 17.23% and 24.5%, respectively, compared with the original sludge. The influence mechanism of APAM and chitosan on the dewatering effect of silt plate and frame filter press was further investigated by particle size analysis, XRD and SEM tests, and the particle analysis test showed that after the addition of APAM and chitosan, the small particles in the silt were bridged into large particle flocs by flocculation, and the d90 increased from 10.97 μm to 29.48 and 29.63 μm, respectively.