The section of Yangtze River downstream Nanjing, where the 12.5 m deepwater channel phase I project is located, is a tidal reach, and ships with a tonnage over 50 000 need to pass in and out by tide. Based on the tidal characteristics of the engineering river reach, the duration by tidal current and the tide-bound water levels are analyzed under conditions of different guarantee rates of first and second tide saving time, from Tiansheng Harbor of Nantong to the Yangtze estuary. Furthermore, the guarantee rate for navigation of container ship, crude oil ship, bulk carriers of different tonnage, and the rationality of the navigation standard of phase I project are demonstrated.