The execution mode of the invention discloses a method for coding data, which is to add additional synchronous heads to data subjected to line coding and FEC coding and then send the data through framing. The execution mode of the invention also provides a corresponding method for decoding the data, a data coder and a data decoder. With the addition of redundant information used for synchronization, the execution mode of the invention can also ensure the synchronous performance of a transmission system under the condition that the line coding selects an algorithm with smaller redundancy; besides, the additionally added synchronous heads do not take part in the FEC coding computation to ensure that the coding gain of the FEC is not affected.