Abstract: A method is proposed for estimating the position of a broadband source in the direct zone of deep water based on a bottom-mounted horizontal array. The method involves matching frequency valleys of the interference structure. First, the longitudinal aperture of the horizontal array is used to obtain the interference fringes, and then the frequency valleys are extracted from the enhanced 1-D interference structure. By incorporating the prior estimated source range, the source depth can be estimated by matching the number and frequency values of valleys. Simulation results demonstrate the robustness of the method against signal spectrum flatness, showing approximately 5 dB higher tolerance to signal-to-noise ratio compared to conventional matched field processing and 1-D interference structure matching method on uneven signal spectrum conditions. Experiments conducted in the deep sea are introduced to verify the proposed method. The localization results of multiple signals indicated that the proposed method still has a good performance for sources with uneven spectrum.