A channel state information reporting method, comprising: obtaining, by a terminal device, first indication information, wherein the first indication information is used to indicate a differential value between channel state information of a first antenna port set and channel state information of a second antenna port set, the first antenna port set comprises x antenna ports of the terminal device, the second antenna port set comprises m antenna ports of the terminal device, the first antenna port set is different from the second antenna port set, and x and m are positive integers; and sending, by the terminal device, the first indication information; wherein the channel state information of the first antenna port set comprises first amplitude information associated with a channel matrix G u of the first antenna port set; and the channel state information of the second antenna port set comprises second amplitude information associated with a channel matrix G d of the second antenna port set, wherein G d is a matrix with m rows and M columns, G u is a matrix with x rows and M columns, and M is a positive integer; wherein the first amplitude information is determined based on an average value of amplitude information of at least two elements of G u, and the second amplitude information is determined based on an average value of amplitude information of at least two elements of G d; or the first amplitude information is determined based on an average value of amplitude information of at least two elements of a matrix W 2, u corresponding to G u, and the second amplitude information is determined based on an average value of amplitude information of at least two elements of a matrix W 2, d corresponding to G d, wherein G u T ( l u) = W 1 × W 2, u ( l u), G d T ( l d) = W 1 × W 2, d ( l d), X T represents transposition of a matrix X, X( l u) represents an l u th column of the matrix X, X( l d) represents an l d th column of the matrix X, W 1 is an M*N matrix, W 2, u is an N*x matrix, W 2, d is an N*m matrix, N is a positive integer, l u ∈ {1, 2,..., x}, and l d ∈ {1, 2,..., m}. obtaining, by a terminal device, first indication information, wherein the first indication information is used to indicate a differential value between channel state information of a first antenna port set and channel state information of a second antenna port set, the first antenna port set comprises x antenna ports of the terminal device, the second antenna port set comprises m antenna ports of the terminal device, the first antenna port set is different from the second antenna port set, and x and m are positive integers; and sending, by the terminal device, the first indication information; wherein the channel state information of the first antenna port set comprises first amplitude information associated with a channel matrix G u of the first antenna port set; and the channel state information of the second antenna port set comprises second amplitude information associated with a channel matrix G d of the second antenna port set, wherein G d is a matrix with m rows and M columns, G u is a matrix with x rows and M columns, and M is a positive integer; wherein the first amplitude information is determined based on an average value of amplitude information of at least two elements of G u, and the second amplitude information is determined based on an average value of amplitude information of at least two elements of G d; or the first amplitude information is determined based on an average value of amplitude information of at least two elements of a matrix W 2, u corresponding to G u, and the second amplitude information is determined based on an average value of amplitude information of at least two elements of a matrix W 2, d corresponding to G d, wherein G u T ( l u) = W 1 × W 2, u ( l u), G d T ( l d) = W 1 × W 2, d ( l d), X T represents transposition of a matrix X, X( l u) represents an l u th column of the matrix X, X( l d) represents an l d th column of the matrix X, W 1 is an M*N matrix, W 2, u is an N*x matrix, W 2, d is an N*m matrix, N is a positive integer, l u ∈ {1, 2,..., x}, and l d ∈ {1, 2,..., m}.