Abstract: To solve the problem of passive detection based on reliable acoustic path using vector vertical array in the deep ocean, a shallow target depth estimation method by matching the broadband complex acoustic intensity interference structure is proposed. This method is based on the image theory, from which the analytical expression for the complex acoustic intensity output of the vertical array is derived. This approach capitalizes on the sensitivity of the vector field frequency interference structure with respect to the source depth in reliable acoustic path. It is employed to determine the optimal depth match, utilizing the complex acoustic intensity output produced by the beamforming of the vertical array. A significant advantage of the proposed algorithm is its independence from the accumulation of target motion states, attributed to its real-time applicability. The simulation results demonstrate that the algorithm significantly improves the signal-to-noise ratio tolerance in comparison to existing depth estimation methods. Moreover, the algorithm exhibits significant robustness in response to environments with fluctuating conditions. The practical efficacy of this algorithm is further validated through the processing of experimental data for target detection in deep sea. The performance of the proposed method is evaluated using data measured by a deep-sea bottom vector vertical array, which receives broadband noise signals emitted by a low-frequency source at various distances and depths.