Abstract: In shallow-water acoustic environments, the warping transform can be used to separate coherent components in the frequency domain. However, passive ranging requires modal orders to be identified based on characteristic frequency peaks. Under negative thermocline conditions, the severe attenuation of lower-order normal modes makes this identification more difficult. This study introduces a dual-depth warping transform method. Using vertical dual hydrophone reception, this method combines the differences in the warping transforms of the cross-correlation functions and the autocorrelation functions at two depths to obtain modal order information. This approach reduces ambiguity in passive ranging. By dividing the signal processing frequency band and integrating wide-band and narrow-band characteristic frequency information, the method enhances passive ranging performance. The position of the main eigenfrequency peaks of the autocorrelation function warping transform differs significantly at the two depths when the vertical correlation coefficients of the coherent components of the acoustic field at the two receiving depths are low, resulting in better performance of the passive ranging method. Conversely, a high vertical correlation coefficient can degrade ranging performance. Both simulation results and experimental data processing results verify the effectiveness of the proposed passive ranging method.