Channel state information (CSI) sending methods, apparatuses, and systems are disclosed. In an implementation, a method comprises: receiving, by a network device from a terminal device, channel state information (CSI) comprising a rank indicator (RI), indication information, and a second precoding matrix indicator (PMI2); determining, by the network device, the RI and the indication information from the CSI; determining, by the network device, the PMI2 based on the RI and the indication information; and determining, by the network device, a precoding matrix W based on the RI and the PMI2, wherein W satisfies W=W1×W2, W is an Nt by L matrix, W1 is an Nt by 2I matrix, W2 is a 2I by L matrix, L is a rank indicated by the RI, Nt is greater than or equal to L, and I is an integer greater than or equal to 1.