Abstract: Irregular repeat-accumulate (IRA) codes have a good performance near Shannon limits under BP decoding algorithm. However, BP algorithm has high complicated operations. To reduced complexity of decoding algorithms, two algorithms namely the sum-min algorithms and piecewise linear approximation algorithms, are proposed. Minimum sum algorithm is very simple and is easy for hardware implementation. But the decoding performance is degraded. Piecewise linear approximation algorithm is a good tradeoff between decoding performance and complexities. Simulation results show that with complexity greatly reduced, piecewise linear approximation algorithm achieve a performance very close to that of the BP algorithm.