Abstract: The existing array invariant methods fail to estimate source-depth and have large range estimation error for the long-source. To solve this problem, a broadband source range and depth estimation method using the array invariant is proposed in this paper. The proposed method firstly converts the wideband received signal into the beam-time domain for mode separation by frequency domain beamforming and Fourier inversion, and then multiple peak positions in the beam-time domain are connected to form the beam-time migration curve. The shape of the curve is determined by the array invariant and is related to the source-range. The energy distribution on the curve is determined by modes excitation factors and is related to the source depth. Then, the proposed method extracts the beam time intensity along the beam-time migration curve, and realizes the source range and depth estimation by matching the beam time intensity. SWellEx-96 experimental data processing results show that the mean relative errors of range and depth estimation in the proposed method are 3.9% and 3.4% respectively, while the mean relative error of range estimation in the conventional array invariant method is 5.1%, which verifies the superior performance of the proposed method.