Based on the salinity advection-dispersion equation, constant-dispersion-coefficient and variable-dispersion-coefficient analytical models for saltwater intrusion in Humen of the Pearl River Estuary were constructed under two assumptions of a constant longitudinal salinity advection-dispersion coefficient and a spatially varying longitudinal salinity advection-dispersion coefficient. With field measured runoff and salinity data, the saltwater intrusion process was simulated and reproduced; the spatiotemporal variation laws of the longitudinal salinity advection-dispersion coefficient were comparatively analyzed, and the salinity dispersion characteristics in Humen were explored. The results indicate that the variation range of the longitudinal salinity advection-dispersion coefficient in Humen is small, and the saltwater intrusion process curve presents a bell-shaped transition form, characterized by convexity in the downstream reach and concavity in the upstream reach; the salinity gradient gradually increases and then decreases along the upstream direction. The salinity dispersion characteristics of the downstream waterway in Humen are significantly affected by the incoming water from the Dongjiang River, showing obvious segmented features. During spring and neap tides, the spatiotemporal average of the longitudinal salinity advection-dispersion coefficient in the downstream waterway of Humen affected by the Dongjiang River is 1 785 m²/s, while the overall spatiotemporal average of the upstream and downstream waterways of Humen is 2 649 m²/s. Huangpuyou Station is a segmented characteristic station of the Humen Waterway. Compared with the value assignment method that comprehensively considers the upstream and downstream dispersion characteristics, adopting the longitudinal salinity advection-dispersion coefficient calibrated for the waterway downstream of Huangpuyou Station in the analytical model can improve the prediction accuracy of the model for longitudinal salinity distribution changes in the reach affected by the Dongjiang River but underestimates the actual length of saltwater intrusion in Humen to a certain extent.