In order to address the issues regarding the high water content, poor dewatering performance, and occupied space of landfill, the physical property tests and experiments on the lake silt samples were conducted. The effects of cationic polyacrylamide (CPAM), lime dosage, and dehydration time on the dehydration performance indexes such as the concentration ratio, the water content, and the decreasing ratio of water content of the lake silt with the initial water content of 91% were investigated. The results revealed that the concentration ratio reached 3.6 times when the dosage of CPAM was 40mg/L, and the water content decreased to 70% and the decreasing ratio of water content decreased to 29% after dehydration for 10min. The concentration ratio was about 2.6 times when the dosage of lime was 3.8g/L, and the water content decreased to 73% and the decreasing ratio of water content decreased to 24% after dehydration for 10min. The variation laws of water content of the lake silt with initial water content of 91%, 85%, and 80% after flocculation concentration dehydration was studied based on the concept of the decreasing ratio of water content. It was concluded that the decreasing ratio of water content was independent of the initial water content. It was only significantly proportional when the dosage of CPAM was 15∼45mg/L and lime was 1∼7g/L. The linear constant depended on the intrinsic properties of the lake silt. According to the variation laws of the water content and the water-hinge hypothesis, the calculation formula of the water content was proposed and the mechanism of critical addition value breaking the silt hinge in flocculation concentration dehydration was formulated.