A method in the embodiments of this application includes: generating, by a terminal device, first information, where the first information includes parameters q, m1, m2, . . . , mL, and indication information of a vector V; q is an integer, and q 1; 0≤ml≤N−1, and 1≤l≤L; L>1, N, L, and l are integers, and N is a quantity of subbands in a frequency domain bandwidth; and the vector V includes L elements and satisfies V=Fq×C, where C is a vector formed by N elements c1, . . . , cN, C=[c1 c2 . . . cN]T, ck is used to indicate channel state information on a kth frequency domain subband, ck is a complex number, a modulus of ck is |ck|≤1, and 1≤k≤N; and sending, by the terminal device, the first information to a network device.