In order to improve the representativeness of data for the calculation of riding high tides in a long waterway at a tidal estuary, this paper presents the multi-station combined method for the calculation. Based on multi-station simultaneous tidal data, and taking the navigational mode, tidal wave propagation and other factors into account, this method can get a reasonable result of riding high tide level in a tidal estuarine waterway. The calculation based on Yangtze Estuary deepwater channel shows that, at the same tide -riding duration and cumulative relative frequency, the riding high tide level needed for a ship to sail into the estuary is bigger than that at a single station alongside, and esp. significantly bigger than that when the ship moving out. The design of a long navigational channel at a tidal estuary should identify a reasonable tide-riding mode according to the nature and strength of tides at local estuary and their comparison with run-off, the characteristics of ships’navigation such as speed, sailing in/out with/without load, and depths along the channel, i.e. to define a suitable tide-riding length of the channel accordingly.