Embodiments of this application provide a channel quality reporting method, an apparatus, and a system. A terminal device determines a first index corresponding to the channel quality, and sends the first index and indication information to a network device, where the first index occupies a first field, the first index is an index in an index set corresponding to a case in which a repetition number of a physical downlink control channel and/or a physical downlink data channel is a first repetition number, and the indication information indicates that the first field is occupied by an index corresponding to the first repetition number.