This application relates to a method for determining a length of an low-density parity-check (LDPC) code word in a ultra-wideband (UWB) system and a related apparatus. The method includes a communication apparatus that determines a length of an LDPC code based on a length of a to-be-encoded information bit. When the length of the information bit ranges from 0 to 324, a 648-bit LDPC code is selected. When the length of the information bit ranges from 325 to 648 or from 973 to 1296, a 1296-bit LDPC code is selected. When the length of the information bit ranges from 649 to 972, a 1944-bit LDPC code is selected. According to embodiments of this application, higher performance gain can be achieved.