One- and two-dimensional coupling model has been developed to analyze the flood inundation aspect of protected lowland. One-dimensional model solves the Saint-Venant equations by the Preissmann method, and two-dimensional model solves the shallow water equation by the integrated finite difference method. The coupling model approximates unsteady supercritical and subcritical flow, backwater flooding effects, and escaping and returning flow from two-dimensional flow model to channel system. The model has been applied to the levee failure in the Nakdong river during September 13 through 15, 2000. Velocity distributions and inundated depths were presented to demonstrate model simulation results.