A channel state information sending method, a channel state information receiving method, and a device are disclosed, to reduce resource overheads required when a terminal device feeds back CSI to a network device in a scenario of a high precision codebook-based precoding matrix. The method includes: determining, by a terminal device, a precoding matrix W; sending, by the terminal device, a signal including CSI to a network device; obtaining, by the network device, an RI and indication information based on the signal including the CSI; obtaining, by the network device, a PMI2 based on the RI and the indication information; and determining, by the network device, the precoding matrix W based on the rank indicator RI and the second precoding matrix indicator PMI2.