On the open coast of the Changjiang Delta, waves temporally play their dominant roles in shaping the tidal-flat profile, especially during typhoons. Detailed analyses are presented of the variations in grain sizes of surface sediments and bed level, measured in the summer of 1999 at Nanhui mudflats, south flank of the Changjiang Delta, China. Cross-shore variations in bed level are distinctly site-specific in response to waves. The site-specific erosion rates are related to local water depth, sediment properties, vegetation, and exposure time per semidiurnal tidal cycle. A great difference exists between the higher and lower intertidal mudflats bordered at the mean sea level (MSL): the higher section is dominated by continuous accretion, while the lower section is characteristic of dynamic changes in erosion and accretion phases. Swells play their more important roles in shaping the profile than local wind-driven waves at the study mudflat, where swells propagate onshore without great barriers’ damping and local winds are not highly strengthened by distant typhoons. Storm processes are greatly modulated by tides. The magnitude of erosion is greater by a weak storm during spring tides than a strong storm during neap tides. Significant changes in entrainment capacity of tidal currents from neap to spring tides account for the different erosion and accretion models of the intertidal mudflat.