Abstract: A fast decoding method for low density parity check (LDPC) code obtains a block from the information received by a digital communication system, and computes the information of a bit node and a check node by a simplified method, and determine the actual value of the bit node from the logarithm likelihood ratio (LLR) estimated value of each bit node. The simplified method of the invention provides a more effective simplified circuit and a faster computation speed than the traditional functions while maintaining the same error code rate as that before the simplification.