An apparatus and a method for reallocating segments in a broadband wireless communication system are provided. An average density for all cells in system and an average minimal inter-cell distance R are computed. A circle is determined having a radius kR and a center at a corresponding cell by increasing a constant k until a density of the circle becomes less than or equal to the average density.A cluster is generated for each cell, which is composed of cells included in the determined circle. Accordingly, segment allocation capability can be improved while minimizing a width of segment reallocation.