Abstract: The properties of incomplete sound channels in the deep sea are significantly influenced by the extensive distribution of submarine hillocks and other small-scale topographic variations on the deep-sea floor. Through the experimental data from the sea area of the South China Sea with hillock topography, it has been found that the topography of submarine hillocks leads to phenomena such as a blurred structure in the convergence zone and abnormal increases or decreases in transmission loss. The mechanism of acoustic propagation characteristic change in the typical region of the experimental sound field is analyzed by numerical simulation, and the influence of deep-sea submarine hillocks under varying conditions of the depth of the sound source and receiver and the frequency of the sound source is further discussed. The results indicate that the transmission loss remains relatively stable in the direct sound zone, the refraction convergence zone, and the shadow zone where sound rays do not interact with the hillocks. However, in the areas where sound rays do interact with the seafloor hillocks, including the shadow zones and the convergence zones for seafloor reflection, the transmission loss exhibits irregular variations in increase or decrease. In addition, the influence caused by submarine hillocks gradually weakens as the source and receiver depths increase, and gradually increases as the frequency (<500 Hz) increases.