Abstract: Spectrum sharing is one of key technologies in cognitive wireless networks. In order to eliminate interference between the authorized primary user and the cognitive user over the frequency selective channels of cognitive wireless networks, a new method of spectrum sharing is presented in this paper. It is made full use in the new method that the channels between different users are not relevant due to frequency selective fading in wireless communication systems; the general solution of the pretreatment matrix is obtained by solving the matrix equation; and both the primary user and the cognitive user transmitter are pretreated in the new scheme. To eliminate the interference between the primary user and cognitive user in cognitive wireless networks while effectively send and receive data. Theoretical analysis and simulation results show that the new method can effectively eliminate the interference between the primary and the cognitive user of two-way to achieve the equality of different users to share radio spectrum resources, which can improve the efficiency of spectrum utilization and alleviate the contradiction between the increasing requirement and the scarcity of spectrum resources at present and in the further. Furthermore, the new method is also applicable to different cognitive users for sharing spectrum.