Abstract: The optimization of spectrum allocation based on protecting licensed link in Cognitive Radio Network is researched. A new model of spectrum allocation based on game theory is presented and a fast convergent spectrum allocation algorithm for protecting licensed link is proposed. The simulation analysis shows that the algorithm has fast convergent speed and achieves spectrum allocation optimization of cognitive radio link based on protecting licensed link; the simulation also presents the relation between network performance parameters and proportional factor, which provides a basis to algorithm application for cognitive radio network with different performance requirement.