Abstract: In this paper, the comparison of bit error ratio(BER) performance of symbol-by-symbol frequency domain differential detection(SS-FDDD) and multiple-symbol frequency domain differential detection(MS-FDDD) in orthogonal frequency division multiplexing system is obtained by simulation, the results indicate that when the whole bandwidth of the symbols used to MS-FDDD is much less than the coherent bandwidth of the channel, the BER performance of MS-FDDD is better than that of SS-FDDD; when the whole bandwidth of the symbols used to MS-FDDD is closed to the coherent bandwidth of the channel, the BER performance of SS-FDDD is better than that of Multiple-symbol frequency domain differential detection.