In this paper, we investigate the energy efficiency and spectrum efficiency, including one-hop device-to-device (D2D) communications mode and two-way ampli-fy-and-forward (AF) relaying D2D commu-nications mode in underlay D2D communica-tions enabled cellular networks. An analysis of average energy efficiency and spectrum efficiency are developed and closed-form expressions are obtained for two types of D2D communications modes under the effect of Rayleigh fading channel, path loss, and co-channel interference. Analytical results are validated through numerical simulations. Based on the simulation, the effects of the interference, the distance between D2D pair and the position of relay node on the energy efficiency and spectrum efficiency of D2D communications are investigated. The optimal D2D transmission powers of these two modes to maximize the energy efficiency are also in-vestigated.