Abstract: The stable range-frequency interference structure(waveguide invariance) for low frequency monostatic bottom reverberation in shallow water is derived theoretically in this paper by using ray-normal mode coherent reverberation model combined with separable bottom scattering model.And a reverberation forecasting and mitigating method based on the waveguide invariance is presented.According to the waveguide invariance,the reverberation intensity for the detecting range can be estimated from the reverberation signals for other ranges with frequency shift.Then the reverberation component for the detecting range can be canceled mostly in the echo intensity,so as to enhance the echo-to-reverberation ratio and improve the detection capability of the active sonar.Simulations in typical horizontal layered shallow water environment showed the stability of waveguide invariance structure in the low frequency monostatic bottom reverberation and the efficiency of the reverberation forecasting and mitigating method based on the waveguide invariance.