Abstract: With the increase of array aperture, the conventional matched field processing is more sensitive to mismatch while obtaining a higher gain. In this paper, the received signal and the data-replica are processed by the difference frequency auto-product at the same time, and the difference frequency matched field processing is used to reduce the sensitivity to mismatch, so as to improve the robustness of the localization. Based on the normal-mode theory, the sensitivities of difference frequency matched field processing and conventional matched field processing to array mismatch and environment mismatch are compared, and the advantages of applying difference frequency matched field to acoustic source localization of large aperture horizontal array in shallow sea are analyzed. The simulation and experimental results show that the difference frequency matched field processing has better localization robustness.