Deep-water channel in Yangtze River reach below Nanjing is located in a tidal reach, and how to calculate its design lowest navigable water level is an essential work to the technical demonstration of its channel construction. According to a preliminary demonstration and analysis, some basic conclusions are obtained as follows:the initial base plane of existing channel depth for Yangtze River reach below Nanjing shall not be regarded as its design lowest navigable water level and it shall not be easily adjusted; its design lowest navigable water level shall be calculated by adopting a recommended method listed in Code of Hydrology for Sea Harbor and is necessarily adjusted in the light of a change in hydrological conditions; the design water depth at very few sections should be larger than 12.5 m.