A channel state information feedback method and a related product are provided. A network device sends first indication information. A terminal device sends second indication information based on the first indication information. The second indication information indicates X groups of basis vectors. The first indication information indicates P groups of basis vectors. The X groups of basis vectors belong to the P groups of basis vectors. Only a basis vector for representing a sub-eigenspace beam needs to be selected from a limited quantity of basis vector groups. In this way, indication overheads of a basis vector for representing a sub-eigenspace beam are reduced, and processing complexity is reduced.