Abstract: Aiming at the limited battery capacity of D2D devices in D2D relay communication, this paper proposes a joint power control and relay selection optimization method to maximize system energy efficiency. First, under the condition that the minimum data rate of the cellular link is satisfied, the power control problem is modeled as a nonlinear programming problem, and the optimal transmission power of the D2D transmitter is solved. Then, the neighboring nodes of the sending node and the receiving node are used respectively. The domain is the radius to establish a spherical model with uniform distribution of nodes. Secondly, based on the path loss similarity, the nodes are iteratively clustered by k-means, and the centroid of the node with the smallest path loss is obtained. Finally, the centroid is used as a relay node for D2D Following the communication. The simulation results show that the optimization method proposed in this paper can maximize the energy efficiency of the system under the condition of ensuring high-quality communication.