An innovative method of cooperative frequency domain differential modulation and demodulation is presented.This method applies the prior knowledge of channel propagation to selecting the variable differential length and carrying out frequency domain modulation.This strategy optimizes the design of system parameters to effectively improve the anti-interference ability of the differential system in time-varied multipath channel circumstance without making the execution more complicating.The simulations and comparisons demonstrate the proposed method is effective,and the results show that it is especially suitable for the fading channel with strong propagation and fast time-variation. An innovative method of cooperative frequency domain differential modulation and demodulation is presented. This method applies the prior knowledge of channel propagation to selecting the variable differential length and carrying out frequency domain modulation. This strategy optimizes the design of system parameters to effectively improve the anti- interference ability of the differential system in time-varied multipath channel circumstance without making the execution more complicating. simulations and comparisons demonstrate the proposed method is effective, and the results show that it is particularly suitable for the fading channel with strong propagation and fast time -variation.