An apparatus and method for transmitting a signal in a communication system using a Hybrid Automatic Repeat reQuest (HARQ) scheme are provided. The method includes generating a codeword vector by encoding an information vector by using a first parity check matrix of Low Density Parity Check (LDPC) codes, generating a transmission vector by processing the codeword vector, and transmitting the transmission vector. When the first parity check matrix includes a plurality of square matrix columns, each square matrix includes a size of L×L, the first parity check matrix is one of p parity check matrixes stored in the signal transmission apparatus, the p parity check matrixes support different numbers of information vector square matrix columns, and each of the numbers of information vector square matrix columns indicates the number of square matrix columns corresponding to the information vector from among the plurality of square matrix columns. The first parity check matrix is a parity check matrix supporting the number of information vector square matrix columns determined by using the length of the information vector and the value L from the p parity check matrixes, and the value L is determined by using p and the length of the information vector.