In broadband power line Multi-input multi-output (MIMO) communication, there are multi-user interference and co-channel interference, which needs an application of a beam forming algorithm to eliminate it. Because the channel state information cannot be accurately acquired, it needs a quantitative feedback for channels, so that the feedback error would cause a decline in performance of the system. Aiming at this problem, this paper proposes a beam forming algorithm, which considers the influences of quantization error of the algorithm. In the premise of ensuring the quality of customer service, this algorithm takes maximizing the system energy efficiency as the optimization goal. The beamforming simulation verifies the effectiveness and robustness of the algorithm.