Embodiments of this application provide a precoding matrix indication method, a communications apparatus, and a storage medium. A precoding matrix of each of K frequency-domain units satisfies W=W1×W2, and elements in W2 in the K frequency-domain units are represented by P elements that are relatively few. A terminal device reports third indication information, where the third indication information includes first indication information and the second indication information, and the first indication information and the second indication information are independently encoded. The first indication information is used to indicate the P elements, and the second indication information is used to indicate P. Therefore, the terminal device can adjust a quantity of information bits of the second indication information based on a channel condition change, thereby improving precoding matrix reporting efficiency.