The present disclosure relates to precoding matrix determining methods, devices, and systems. In one example method, a receive end device obtains channel state information (CSI) of a first channel and information about P antenna port groups of a transmit end device. The receive end device determines V orbital angular momentum (OAM) mode groups based on the CSI of the first channel and first OAM modes, determines a first precoding matrix based on the P antenna port groups of the transmit end device and the V OAM mode groups, and sends, to the transmit end device, first indication information indicating the first precoding matrix. The transmit end device receives the first indication information, and determines the first precoding matrix based on the first indication information.