Abstract: Two kinds of passive ranging algorithms are proposed combined with waveguide invariant theory based on the important characteristic of the ocean waveguide that the interference structure is stable and can be observed in the low-frequency acoustic field,in order to explore the passive ranging method suitable for the towed line array sonar.The double arrays(elements) model is adopted,so the LOFARgram and bearing-time records of the each array(element) can be obtained.Then the frequency-time records can be extracted by processing the LOFARgram via Radon transform,so the passive ranging can be achieved combined the corresponding ranging algorithms.And the feasibility of the algorithms has been verified by simulation researches and positioning accuracy analysis.