A channel state information reporting method and apparatus are described. The method can include a terminal device obtaining first indication information and sending the first indication information to a network device. The network device receives the first indication information, where the first indication information indicates 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 includes x antenna ports of the terminal device, the second antenna port set includes m antenna ports of the terminal device, and the first antenna port set is different from the second antenna port set. The channel state information reporting method and apparatus in embodiments of this application help improve accuracy of channel state information obtained by a network device, and improve data transmission performance.