Multipath interference is the main threat to the ultra-low targets detection. A novel method of suppressing multipath interference based on Brewster Effect is proposed. The traditional Four-Path Model is modified by complex reflection coefficient and antenna pattern. The numerical hybrid method PO+MEC is used to calculate the scattering fields of targets. The method based on scattering center model is introduced to generate the echo signal. The effect of the method proposed in this paper is analyzed and proved in two aspects, scattering field and echo signal. The conclusion is that, if the active seeker detect the ultra-low target using the Brewster angle as the grazing angle in VV-polarization, the multipath interference is well suppressed. Under maritime environment, the Brewster angle is approximate 7 . The work in this paper is of great significance in military field.