A measurement method, a terminal device, and a network device are described. The measurement operation includes sending a channel state information-reference signal CSI-RS measurement beam to a terminal device. The CSI-RS measurement beam is obtained by the network device by weighting a CSI-RS by using a beamforming weight, and the beamforming weight is used to perform beamforming on the CSI-RS. The measurement operation further includes receiving a rank indicator and a channel quality indicator that are determined based on the CSI-RS measurement beam. The measurement operation further includes weighting and transmitting a downlink channel based on the rank indicator and the channel quality indicator. The CSI-RS is weighted and transmitted by using the beamforming weight, to help improve accuracy of rank measurement, thereby improving a user throughput.