A variable sub-carrier mapping method comprising steps of: applying different bit interleaving schemes to different transmissions of a hybrid automatic retransmission request (HARQ) process in side of transmitter; and in the side of the transmitter, modulating symbols onto sub-carriers for transmitting. Different transmissions in one HARQ process adopt different bit interleavers or different symbol-to-sub-carrier mapping methods so as to realize that the same bit of different transmissions in one HARQ process is transmitted via different sub-carriers. Therefore, the system achieves the frequency diversity gain and reduces the probability of failure of HARQ transmission caused by that some bits are always transmitted via the sub-carrier with the same deep fading. In this way, the average HARQ retransmission times can be reduced and the system throughput can be improved.