Based on the characteristics of hydrodynamics and sediment transport in the bar area in the Modaomen Estuary, a flume experiment was performed to study the evolution of the longitudinal profile of the mouth bar. The mouth bar evolution was investigated under the impacts of floods with different ret periods as well as flood-wave interaction. The results showed that floods with different ret periods had significant influences on the evolution of the river mouth bar. Particularly on the inner slope of the mouth bar, the sediment was substantially active and moveable. The inner slope and the bar crest tended to be remarkably scoured. The erosion was intensified with the increase of the magnitude of floods. Moreover, the bar crest moved seawards, while the elevation of the bar crest barely changed. Under the flood-wave interaction, a remarkable amount of erosion on the inner and outer slopes of the mouth bar was also found. The seaward displacement of the bar crest under the interaction of floods and waves was less than it was under only the impact of floods, while more deposition was found on the crest of the mouth bar in this case.