DevicetoDevice（D2D） communications can effectively improve the network capacity. A capacity optimization method based on multipopulation genetic algorithm (MPGA) is proposed, which deals with the number of terminals that can be accommodated in D2D communications. As the traditional cellular network mobile terminals have interference on the D2D users, and the D2D terminals which reuse the same frequency introduce interference each other, it affects the number of accessible D2D terminals. The MPGA based scheme proposed in this paper can adjust the resource allocation scheme quickly, effectively reduce interference under the same frequency, and improve the number of terminals which can be accommodated in the network. The simulation results show that the resource allocation scheme based on MPGA can allocate the reasonable channel resources quickly to reduce the total interference in the system. Besides, it can also improve the number of accessible terminals and the network throughput simultaneously.