An encoding method includes: receiving, by an encoder, an information for encoding; generating, by the encoder, a first portion codeword according to a first encoding rule and the information for encoding, wherein the first encoding rule is an encoding rule configured to generate LDPC code; generating, by the encoder, a second portion codeword according to a second encoding rule different from the first encoding rule and a double check region of the first portion codeword; and concatenating, by the encoder, the first portion codeword and the second portion codeword to generate a codeword. A plurality of trapping sets corresponding to the first encoding rule include at least one error bit within the double check region.