A data transmission method and a communication apparatus. A first device may determine a second sequence, where the second sequence is obtained based on a base sequence and a first mask, and the first mask corresponds to a first encoding scheme. The first device sends the second sequence and a first sequence, where the first sequence includes a first encoded bit sequence obtained by encoding an information bit sequence based on the first encoding scheme, the first encoded bit sequence includes N bits, and N is a positive integer. The second device receives the second sequence and the first sequence from the first device and processes the received first encoded bit sequence by using a decoding scheme corresponding to the first encoding scheme. This manner is applicable to long-distance data transmission and may reduce missed detection and false detection of the first encoded bit sequence.