A power and subcarrier assignment algorithm is proposed in this paper for maximizing the energy efficiency in the single-relay multi-users orthogonal-frequency-division-multiplexing(OFDM) systems. Under the constraints of maximum total power and minimum transmission rate, we formulate a joint optimization scheme for subcarrier pairing and power allocation to maximize the energy efficiency. The Dinkelbach’s method is used to depress the complexity and to transform the problem to a linear programming, then we use the dual decomposition approach solve the problem. In the premise of the system transmission rate, this algorithm uses the improved decode-and-forward(IDF) relay to maximize the system energy efficiency. Simulation results illustrate that,compared with the spectral-efficient maximization(SEM) algorithm, the energy-efficient maximization(EEM) algorithm proposed in this paper makes the energy efficiency not decline when the signal-to-noise radio(SNR) is at a high level. At the point where SNR is 10 d B and the number of subcarriers is 16, system energy efficiency is increased by 6.2% and 11.9% with the subcarrier pairing strategy and power allocation strategy respectively. A power and subcarrier assignment algorithm is proposed in this paper for maximizing the energy efficiency in the single-relay multi-users orthogonal-frequency-division-multiplexing (OFDM) systems. Under the constraints of maximum total power and minimum transmission rate, we formulate a joint optimization scheme for subcarrier pairing and power allocation to maximize the energy efficiency. The Dinkelbach’s method is used to depress the complexity and to transform the problem to a linear programming, then we use the dual decomposition approach solve the problem. In the premise of the system transmission rate, this algorithm uses the improved decode-and-forward (IDF) relay to maximize the system energy efficiency. Simulation results illustrate that, compared with the spectral-efficient maximization ) algorithm proposed in this paper makes the energy efficiency not decline when the signal-to-noise radio (SNR) is at a high level. At the poi nt where SNR is 10 d B and the number of subcarriers is 16, system energy efficiency is increased by 6.2% and 11.9% with the subcarrier pairing strategy and power allocation strategy respectively.