Taking the Qiantang River Estuary as an example, this research employed a two-dimensional horizontal saltwater intrusion model capable of simulating tidal bore phenomena to investigate saltwater intrusion in a strong tidal bore estuary. By modifying the tidal level processes at the model’s seaward boundary to represent variations in offshore tides, the study examined the influence mechanisms of three tidal characteristic parameters, high tidal level, low tidal level, and tidal range, on saltwater intrusion in the estuarine region. The results indicate that offshore tidal changes primarily affect the extent of saltwater intrusion through variations in high tidal levels, while changes in low tidal levels have minimal impact. Therefore, it is inadequate to only use the tidal range index to reflect the influence of offshore tidal variations on estuarine saltwater intrusion. In addition, estuarine saltwater intrusion responds rapidly to offshore tidal changes, with effects persisting for more than three tidal cycles.