The drainage consolidation characteristics of municipal sludge are closely related to its water occurrence form. However, there is insufficient understanding of the water transformation law of municipal sludge after chemical conditioning and consolidation. Based on the theory of soil science, the soil-water potential curves of different types of municipal sludge were tested by centrifuge method, and the water forms of municipal sludge were divided into bound water, capillary water and gravitational water according to the range of soil-water potential. On this basis, the different forms of water content in the original sludge, consolidated samples and conditioned sludge samples were compared to reveal the water transformation law of municipal sludge under the action of consolidation and chemical conditioning. The results show that the bound water content of the sludge is reduced by 70% ~ 80% and the free water content is doubled after the sludge is modified by ionic salt. Under the consolidation pressure of 3.1 kPa, only a part of gravity water is discharged from different types of municipal sludge, and the contents of capillary water and bound water are basically unchanged. Under the consolidation pressure of 100 kPa, the gravity water is completely discharged, the capillary water is significantly reduced, and the bound water is slightly reduced.