Aiming at the low energy efficiency caused by the energy consumption of cognitive radio network, an optimal power allocation algorithm is proposed to maximize the energy efficiency of secondary user system based on clustering cooperative spectrum sensing. By establishing the energy efficiency maximization transmission model and considering transmission power, perceived time constraints and interference constraints, the optimal transmitted power allocation algorithm can be obtained to achieve the purpose of the system energy efficiency maximization through using Lagrange function and KKT condition. Then the influence of different parameters on energy efficiency is analyzed. Simulation results show that the proposed algorithm can reduce energy consumption and improve energy efficiency.