The designed lowest navigable water level is an important technical parameter to determine the navigable conditions of the waterway in dry season and ensure the navigation safety of ships.It should be adjusted in time according to the changes of hydrological conditions of the river waterway.Based on the observation data of Nanjing water level station from 1986 to 2024,this paper studies the relationship between the multi-year monthly average water level variation and the multi-year average tidal range in the Nanjing section of Yangtze River main trunk,and demonstrates the tidal reach attribute of the Nanjing section.By employing the comprehensive duration curve method and the assurance rate frequency method for separate derivation and comparison,the designed lowest navigable water level is obtained.The research shows that the Nanjing section belongs to the perennial runoff section of the tidal waters of inland rivers and the water level in Nanjing is mainly affected by runoff.Taking the relatively low comprehensive duration curve method calculation value of 0.55 m as the designed lowest navigable water level,is in line with the recent improvement of waterway conditions and conducive to enhancing the capacity of the waterway during the dry season,meeting the needs of the economy and society development along the Yangtze River to fully utilize the endowment of waterway resources and promote cost reduction and quality improvement of transportation and logistics.The research results provide a reference basis for waterway maintenance of the Nanjing section and the design of related engineering projects.