The invention provides a data processing method coded and decoded by FEC, and a relative device. The method comprises: carrying out FEC coding on a FEC code processing sub-layer for a data code block sequence which is output by a physical code sub-layer and uses m data code blocks as a group, to generate n FEC check code blocks; respecitively distributing m*t2 data code blocks and n*t2 FEC check code blocks to M virtual channels of a first virtual channel group and N virtual channels of a second virtual channel group, wherein m*t2 is less than or equal to m_max, m_max is t1 times of M, n is less than or equal to n_max, n_max is t1 times of N, and m, n, t1 and t2 are positive integers; and respectively multiplexing data distributed to the first virtual channel group and the second virtual channel group onto at most H interfaces of a fisrt physical channel group and at most K interfaces of a second physical channel group according to bit speed-changing multiplexing, wherein M is integral multiple times of H, and N is integral multiple times of K.