Embodiments of the present invention disclose a signal transmission method, a system, and a device. When measuring a reference signal and determining channel quality, UE obtains a difference between codeword to CSI-RS mapping relationships by using a channel quality measurement model, may calculate an optimized mapping relationship by means of measurement, and determines at least one mapping relationship from these mapping relationships, to adjust a codeword to CSI-RS mapping relationship of a channel, thereby improving system flexibility and increasing channel resource utilization.