Abstract: The low-frequency line spectrum radiated by underwater targets contains critical velocity and distance information. This study investigates the use of interference characteristics from cross-correlation of line spectrum to estimate a target’s radial velocity under single-platform observation conditions, with analysis of factors influencing estimation accuracy. An analytical solution for target distance is derived based on radial velocity and azimuth, and its applicability is thoroughly examined. An optimized distance estimation method is proposed, leveraging redundant information from multiple line spectra to significantly reduce errors compared to single line spectrum approaches. The algorithm’s performance is validated through simulations and experimental data. Simulation results demonstrate effective estimation of long-range moving target distances, achieving a relative error below 8%. Application to the SWellEx-96 experimental dataset confirms good agreement between estimated and theoretical values, with relative errors under 10% within the 2−9 km range. Due to its computational efficiency and high timeliness, this method shows potential for practical engineering applications in underwater target localization.