Abstract: This paper focuses on the resource allocation problem in OFDM-based Decode-and-Forward (DF) relay link to maximize Energy Efficiency (EE). Different from the exiting researches that minimizing the transmission power under constant date rate or maximizing the EE without constraints, for considering the circuit power consumption, the optimization problem is formulated as maximizing EE under the constraints of the minimum rate requirements and respective transmission powers of the Source node (S) and Relay node (R) while considering the subcarriers paring problem, which is an optimally joint subcarriers pairing and power allocation problem. It is proved that the optimal energy-efficient solution under the constraints for the OFDM-based relay link is globally unique. Furthermore, a low complexity resource allocation scheme is proposed to solve the formulating joint optimization problem. The simulation results show that the proposed scheme can adaptively allocate power resources under the constraints of the minimum data rate and maximum transmission powers of S/R nodes, and achieve the optimal energy efficiency, which also reduces the outage probability of the transmission link.