Disclosed are an apparatus and a method for reducing the coding complexity in an LDPC code used in a digital communication system. In the method, parameters required for coding are determined according to a coding rate and a code length, a seed matrix is generated according to values of the parameters, a plurality of cell matrices are generated according to the values of the parameters, a parity check matrix is generated using the seed matrix and the cell matrix, and information bits are coded from the parity check matrix. The method can be realized by a small memory and a simple shift register and can perform coding even without obtaining a generation matrix, thereby remarkably reducing the complexity of a system.