Abstract: The passive detection is realized by using a statistical invariant feature of underwater acoustic channel (waveguide invariant). The proposed method needs two sensors at least to calculate the motion parameters. LOFARgrams analysis is made for broadband noise signals which are respectively received by the two sensors. To get the estimation values of waveguide invariant and parameters of curve, HOUGH conversion is used for parameter estimation of LOFARgrams. Then the moving target's angle, distance and speed are estimated according to geometrical relationship. The method has been employed to process the LOFARgrams obtained from Acoustic Toolbox simulation, and the estimated results of target parameters show the validity of the method.