Abstract: In this paper a method used for correcting the coordinates of an underwater moving target obtained by a hyperbolic locating system with a small plane array when the sound velocity varies with depth is reported.This is an iteration method useing a series of differential difference equations to determine iterative values.The results calculated by this method show that under+he same condition,the location error is about several meters or tens of meters without the correction and less than 0.5m with the correction.The method can apply to various types of arrays