Abstract: The dredging project in the Qiantang river was an important water conservancy measure forpreventing tidal waves throughout the Kangxi, Yongzheng and Qianlong reigns in the Qing dynasty. Thispaper systematically analyzes the environmental background, decision-making process and implementation process of the dredging project in the Qiantang river in Qing dynasty, and analyzes the different concepts of water management of the three emperors. Emperor Kangxi took dredging the river as an auxiliary measure to protect against tidal flooding, which was stopped as the tidal inundation subsided. Emperor Yongzheng firmly pushed forward the river diversion project, hoping to change the river channel and tidal situation. Emperor Qianlong devoted himself to the construction of the seawall, but he vacillated on the diversion project. The different attitudes among emperors Kangxi, Yongzheng and Qianlong reflected the transition of tide defense strategy in Qiantang River in the Qing dynasty. The Qiantang River dredging project and seawall construction were mutually beneficial but there were also tensions: while the dredging project alleviated the pressure on the north shore seawall, the construction and management of the dredging project itself dispersed the funds, manpower and energy for the prevention of tidal flooding.