Abstract: When the depth relationship between source and receiver is unknown, using the time delay differences for distance and depth estimation may result in a pseudo source. To address the issue, a method for directly estimating distance and depth using four time delay differences has been proposed. This method analyzes the relationship of four time delay differences between four multipath, by utilizing the difference in the same time delay difference between the pseudo source and the true position, a fuzzy plane is constructed for localization. The pseudo source can be eliminated without determining the depth relationship between the source and receiver, which can be achieved on a single hydrophone. The effectiveness of the method is verified through simulation experiments and error analysis. The sea experiment shows that the method successfully achieves distance and depth estimation of targets ranging from 11.0−16.5 km on two single hydrophones at different depths, with root mean square errors of less than 1.1 km and 54 m, respectively.