Abstract: The formulae for calculating the ocation error of a hyperbolic locating system are deduced. The error sources and their weight are analysed. For an underwater array with short base-lines, the location error of the system caused by the measuring errors of sound velocity, time difference and coordinates of the array elements and by ray bending is calculated. For an underwater array with long base-lines, the accuracy range of location is found. The above results are valuable for reference in determining the error distribution of the hyperbolic locating system.