Abstract: Aiming at the problem that the convergence time of the bearings-only target motion analysis method is long,a modified bearings-only target motion analysis method based on frequency β-warping transform in shallow water is proposed.This method extracts the time delay which is proportional to the target range from the acoustic interference structure using the frequencyβ-warping transform in order to estimate the distance characteristic,and then modifies the bearings-only extended Kalman filter using the linear constraint of state vector derived from the distance characteristic.The numerical simulation results show that,when the signal-to-noise ratio is no less than 8 dB,compared with the conventional bearings-only extended Kalman filter algorithm,the improved algorithm shortens the convergence time of range from 26.5 min to 11.5 min for the target with a uniform speed in a straight line.In a range-independent shallow water waveguide,this method can estimate the distance characteristic quickly and stably,track the target reliably.