Abstract: Using the model of travelling ionospheric disturbances(TIDs), the Doppler shift causing by different scales TIDs is simulated, and the spread of land or sea clutter spectrum and its effects on ship detection for over-the -horizon radar (OTHR) are analyzed. The result indicates that for small-scale TIDs, the amplitude of Doppler shift is small but changes rapidly, and the S-shaped distortion is obvious, which have an impact on OTHR mainly presented the Doppler shift. Doppler shift caused by mesoscale and large-scale TIDs is slightly larger than that caused by small-scale TIDs, but it is changed meditatively with time, and the S-shaped distortion is weakened. Besides the sea clutter Doppler shift, it causes clutter spectral spread and affects the ship detection. Meanwhile, the suppression method for frequency shift and spread caused by different scale TIDs is simulated. And the simulation results show that the algorithm is effective.