Abstract: An adaptive dynamic spectrum allocation scheme among multi-cells in cognitive radio system is proposed. Firstly, the method presents the predicting scheme of idle period of each licensed spectrum units that can be used by cognitive radio, based on this, a dynamic spectrum allocation scheme is proposed to reduce the spectrum handoff ratio and minimize the continuity of the spectrum used by the cognitive radio, which can avoid increment of system overhead and complexity of spectrum management. And the proposed scheme introduces graph theory of coloring to avoid interference among multi-cells. And results of simulation and analysis prove this conclusion.