By analyzing the existing cognitive network models, this paper proposes a cognitive network model in which the primary receiver is treated as a center. This solves the irrationality problem when modeling the interference region where the primary transmitter is treated as a center. Using the proposed model and the information theory, we obtain mutual quantitative restriction correlation of the primary user communication radius, cognitive user density and throughput of primary user under the condition of lowest throughput and communication interruption probability of primary users. Numerical simulation results show that the model is reasonable and effective when a primary receiver is interfered by cognitive users.