Power consumption caused by radio frequency (RF) chains in millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems can be solved by beam selection. However, the spectral efficiency of traditional beam selection algorithms is unsatisfactory due to the reduction in the number of RF chains and the multiuser interference. This work proposes a differential evolution (DE)-based beam selection algorithm and an improved QR precoder to reduce power consumption and increase the performance of the systems. The proposed algorithm selects the optimal beams with DE-based beam selection for each user, which reduces the power consumption and the interference among each beam. In addition, to greatly decrease the multiuser interference, we propose an improved QR precoder by equalizing diagonals and using Tomlison-Harashima (TH) theory which can greatly reduce the computational complexity and improve the performance. The simulation results show that the proposed scheme outperforms some existing algorithms in the aspects of energy efficiency and spectral efficiency.