Dredged mud from Hengsha island in Shanghai was improved by curing agent combining exciting agent and bonding agent such as cement and lime. Permeability tests were designed to study the permeability of the improved dredged mud in the presence of different curing ages and curing agent dosages. The relations of permeability coefficient of solidified dredged mud vs. curing agent content and curing time were analyzed, and the law of changes in permeability coefficient was obtained. Furthermore, the microstructure of solidified dredged mud with different curing agent contents and curing ages was observed by Scanning Electron Microscope (SEM) and the SEM images before and after solidification were obtained. According to the SEM images, changes in the microstructure of dredged mud before and after solidification were compared and analyzed. Results show that the permeability coefficient of solidified dredged mud decreased obviously with the increase of curing agent content and curing age; while under the same curing age, permeability coefficient changed little when curing agent content kept increasing. Micro-structure analysis indicates that calcium silicate hydrated (C-S-H), Ca(OH)₂ crystal, CaCO₃ crystal, amorphous aragonite and ettringite which could fill the pores were found in solidified dredged mud. Moreover, the mechanism of solidification of dredged mud was also analyzed from microscopic viewpoint.