This application discloses a precoding matrix index (PMI) reporting method, and related communications apparatus and medium. The method includes: determining an rank indicator (RI) and a PMI, where the PMI is used to determine R precoding matrices W1, . . . , WR. An rth precoding matrix Wr in the R precoding matrices satisfies Wr=W1×W2,r, where an lth row of W2,r is obtained by performing DFT transform on an lth row of a matrix V2,r, and R is indicated by the RI. The PMI includes first indication information and second indication information. The first indication information includes location index information. The location index information is used to indicate Km,r element locations tr,m,1, . . . , ∈{1, . . . , T} on an mth row of V2,r. The second indication information is used to indicate Km,r complex coefficients at the element locations tr,m,1, . . . , on the mth row of V2,r. V2,r is determined based on the Km,r element locations and the Km,r complex coefficients.