An encoding configuration method includes an optical network unit that receives first information, where the first information indicates a change amount of forward error correction codeword information relative to first forward error correction mother code. The optical network unit determines the forward error correction codeword information based on the first information. According to technical solutions provided in this application, the change amount of the forward error correction codeword information relative to the first forward error correction mother code is indicated, to help implement flexible configuration of the forward error correction codeword information.