Abstract: In order to meet the needs of next-generation wireless communications, based on the asymmetric millimeter-wave massive multiple-input multiple-output (MIMO) system architecture proposed recently, the channel characteristics of asymmetric millimeter-wave massive MIMO systems-channel asymmetry are studied. According to the asymmetric millimeter-wave massive MIMO system architecture and the main factors affecting the asymmetry of the millimeter-wave channel, a new parameter describing the asymmetry of the uplink and downlink channels-the asymmetry factor is proposed. At the same time, a ray tracing platform developed by the laboratory is used to simulate and analyze asymmetric millimeter-wave channels. The results show that the different configuration of the base station transceiver antenna array is the basic reason of channel asymmetry. The complex propagation environment makes this asymmetry more prominent. In severe cases, the asymmetry factor in indoor scenario can reach about −30 dB. At the same time, the cumulative distribution function (CDF) of asymmetric factor in the outdoor line-of-sight (LoS) and non-line-of-sight (NLoS) scenarios fits well with the Gaussian distribution, and the asymmetric factor in the NLoS scenario is obviously smaller than that in the LoS scenario. Therefore, the asymmetry factor can intuitively describe the asymmetry degree of the uplink and downlink channels in different scenarios, and the analysis of the asymmetric millimeter-wave massive MIMO system channel characteristics should also be scenario-oriented.