A decoding method of a cyclic code decoder includes the machine-implemented steps of: establishing a lookup table; receiving a codeword; computing a syndrome and a Hamming weight; if the Hamming weight is not equal to zero and not greater than an error correcting capability value, performing a first error correcting operation; if the Hamming weight is greater than the error correcting capability value, and if the syndrome has a matching syndrome pattern in the lookup table, performing a second error correcting operation; if a second Hamming weight corresponding to a syndrome difference is smaller than a check value, performing a third error correcting operation, otherwise performing a fourth error correcting operation; and if a counter value is greater than zero, performing a fifth error correcting operation before decoding a corrected codeword.