Abstract: Passive source range estimation based on warping transform in shallow water with a thermocline is studied.When the source is above the thermocline, or both the source and the receiver are below a weak thermocline, the sound field is mainly composed of reflective modes. And passive range estimation could be achieved by using time domain warping transform of the autocorrelation function of the received signal. When both the source and the receiver are below a strong thermocline, the sound field is mainly composed of refractive modes. And frequency domain β-warping transform could be introduced to achieve passive range estimation. What's more, when a guided source existing, the estimated ranges match well with the real ones, as long as the estimated waveguide invariant is within a reasonable range. Finally, passive range estimation based on warping transform is applied to broadband data collected during a summer experiment. The estimated ranges match well with the real ones.