A transmit diversity method, a device, and a system are described herein. The method includes: measuring, by a second network device, channel state information based on a pilot signal, and sending rank index information and precoding matrix index information to a first network device based on the channel state information; receiving, by the first network device, the rank index information and the precoding matrix index information that are sent by the second network device; determining a diversity coding scheme based on the rank index information; determining a precoding matrix based on the precoding matrix index information; and performing transmission processing on to-be-transmitted data based on the diversity coding scheme and the precoding matrix.