The USBL acoustic positioning system is a precision instrument which is widely used in marineengineering and underwater unmanned systems. In order to improve the positioning accuracy for underwater targets,the system needs to be calibrated before using. This paper describes a calibration method of USBL acoustic positioning system based on iterative correction of least square method. Through the means of multiple iterativecorrection, this method adopts the least square method as the basic principle to calibrate the translate deviationbetween the base array and the GPS antenna and the rotation deviation between the base array and the compass ,thereby improving the measurement accuracy of the system. Finally, the effectiveness of the method was verified bylake trials.