This paper studies the optimization algorithm of power allocation in decodeandforward OFDM twohop relay links aiming to maximize the energy efficiency of the system. First, the circuit power consumption of the system is taken into account and modeled as a linear increasing function of the rate. Then, under the condition of satisfying the rate and bit error rate, the energy efficiency optimization objective function is established. Finally, based on convex optimization theory, the optimal modulation and power allocation of optimal energy efficiency are obtained. The simulation results show that the proposed power allocation algorithm can lead to the optimum energy efficiency.