Abstract: In the study of medium-frequency and high-frequency acoustic scattering from ducts with cavity structures, formulae for calculating their multiple scattering based on an iterative physical acoustics method are introduced and derived. The formulae can accurately and efficiently solve the high-frequency sound scattering problem in such cavity structures, as verified by numerical simulations and experimental measurements on a JD7704 duct. In addition, by analyzing the distance-angle spectrum of the scattered echoes, the unique multiple scattering interference characteristics of the duct structure are observed, and the mechanism of their formation is explained in detail. On this basis, taking the NACA0012 profile duct as an example, the effects of different profile thickness, curvature, and angle of attack on the duct target strength are analyzed using the iterative physical acoustics method. The research results show that the first-order echo of a duct accurately reflects its external contour characteristics. The high-order echo appears as multiple bright lines beyond the external contour due to the increase in the propagation path of the sound wave in the cavity, reflecting the characteristics of its internal cavity structure and providing identifiable fine features for underwater target identification.