A method includes: parsing a bitstream to obtain an index value of a candidate motion vector list; constructing the candidate motion vector list, where the candidate motion vector list includes candidate motion vectors of K control points of a current block, the candidate motion vectors of the K control points are obtained based on a 2N-parameter affine transform model used for a neighboring block of the current block, N, K are integers greater than or equal to 2 and less than or equal to 4, and N is not equal to K; determining, in the candidate motion vector list, target candidate motion vectors of the K control points based on the index value; and obtaining a predicted motion vector of each subblock of the current block based on the target candidate motion vectors of the K control points. It helps improve coding efficiency in an audio and video coding process.