An FEC decoding apparatus for iterative decoding of groups of codewords, wherein FEC decoding on a group of codewords is performed after FEC decoding of another group of codewords and a codeword is part of the group and the another group, wherein the apparatus comprises: - an obtaining unit, configured to obtain the group, comprising a preset quantity of code words; - a first detection unit, configured to detect whether each code word in the obtained group carries a successfully decoded flag and if yes triggers a decision unit and if no triggers a second detection unit; - the decision unit is configured to perform a sign bit decision on the obtained group, wherein the sign bit decision is to decide a nonnegative number to be 1, and to decide a negative number to be 0; - a third adding unit, configured to add a decided flag to each code word in the obtained group, on which the sign bit decision was performed, to indicate that the sign bit decision has been performed on the code word; - a second detection unit, configured to detect whether there is at least one code word that carries a decided flag in the obtained group; and if yes, triggers a restoration unit, and if no, triggers a second decoding unit; - the restoration unit, configured to perform data restoration on each code word carrying a decided flag, wherein the data restoration is to restore 0 to a negative number of a maximum value obtained after analog-to-digital conversion, and to restore 1 to a positive number of the maximum value obtained after analog-to-digital conversion; and - a first decoding unit, configured to construct a restored group by using each code word obtained after the data restoration and each code word on which the sign bit decision has not been performed and to perform FEC decoding on the restored group; and - a change unit, configured to change the decided flag of each code word on which the sign bit decision has been performed to an undecided flag; - a first checking unit, configured to calculate a checksum of each code word obtained after FEC decoding in the restored group; and - a first adding unit, configured to add a successfully decoded flag to a code word whose checksum after FEC decoding is 0 in the restored group; wherein the apparatus further comprises: - the second decoding unit, configured to perform FEC decoding on the obtained group if no code word carries the decided flag in the obtained group; - a second checking unit, configured to calculate a checksum of each code word obtained after FEC decoding in the obtained group; and - a second adding unit, configured to add a successfully decoded flag to a code word whose checksum after FEC decoding is 0 in the obtained group. - an obtaining unit, configured to obtain the group, comprising a preset quantity of code words; - a first detection unit, configured to detect whether each code word in the obtained group carries a successfully decoded flag and if yes triggers a decision unit and if no triggers a second detection unit; - the decision unit is configured to perform a sign bit decision on the obtained group, wherein the sign bit decision is to decide a nonnegative number to be 1, and to decide a negative number to be 0; - a third adding unit, configured to add a decided flag to each code word in the obtained group, on which the sign bit decision was performed, to indicate that the sign bit decision has been performed on the code word; - a second detection unit, configured to detect whether there is at least one code word that carries a decided flag in the obtained group; and if yes, triggers a restoration unit, and if no, triggers a second decoding unit; - the restoration unit, configured to perform data restoration on each code word carrying a decided flag, wherein the data restoration is to restore 0 to a negative number of a maximum value obtained after analog-to-digital conversion, and to restore 1 to a positive number of the maximum value obtained after analog-to-digital conversion; and - a first decoding unit, configured to construct a restored group by using each code word obtained after the data restoration and each code word on which the sign bit decision has not been performed and to perform FEC decoding on the restored group; and - a change unit, configured to change the decided flag of each code word on which the sign bit decision has been performed to an undecided flag; - a first checking unit, configured to calculate a checksum of each code word obtained after FEC decoding in the restored group; and - a first adding unit, configured to add a successfully decoded flag to a code word whose checksum after FEC decoding is 0 in the restored group; wherein the apparatus further comprises: - the second decoding unit, configured to perform FEC decoding on the obtained group if no code word carries the decided flag in the obtained group; - a second checking unit, configured to calculate a checksum of each code word obtained after FEC decoding in the obtained group; and - a second adding unit, configured to add a successfully decoded flag to a code word whose checksum after FEC decoding is 0 in the obtained group.