The construction of a tidal flat in shallow sea area is a difficult work, because the construction barge is hard to enter to the area where dry and wet condition repeatedly changes dependently on tides. Although the design condition of the tidal flat shape was managed to be constructed by careful works, the deformations by wave actions and the consolidations of the topography have been reported. According to this situation, new concept to form tidal flat in ‘self-design’ process, in which the shape of a tidal flat is allowed to deform by natural process due to waves, is introduced. In this study, the property of tidal flat deformation was studied by 2D wave flume model test. As for the flat shape of the initial topography, a berm was formed at the tip of tidal flat, moved to the shore, resulting in the formation of a tidal flat topography. This result shows that tidal flat can be formed by the self-design process under natural wave actions.