Given the fact that the relay contributes to higher data rate or more reliable transmission at the expense of extra power consumption, we investigate the performance of relay aided Device-to-Device (D2D) communications from the perspective of energy efficiency (EE). Firstly, a closed-form expression for the EE of the considered network over Nakagami-m fading channels is derived. Then, taking into account the effects of practical modulation and coding schemes, we propose a channel quality indicator (CQI) based power control approach to maximize the EE of relay aided D2D communications while guaranteeing the interference limitation. The proposed scheme could avoid unnecessary power increment and is applicable in real time resource allocation. Simulation results demonstrate the validity of the theoretical analysis and illustrate that the CQI based scheme can improve EE.