This application provides an uplink precoding indication method and a communication apparatus. The method includes: A terminal device receives first information from a network device, where the first information indicates M predefined codewords, transmit antenna ports corresponding to any one of the M predefined codewords are fully coherent, and M is a positive integer. In addition, the terminal device determines, based on the first information, a first uplink precoding matrix used by the terminal device to send uplink data, where a quantity of transmit antenna ports corresponding to the first uplink precoding matrix is greater than a quantity of transmit antenna ports corresponding to any one of the M predefined codewords. According to the method, an uplink precoding matrix applicable to more transmit antenna ports can be flexibly indicated, thereby effectively improving uplink transmission performance.