The Ultra-Short Baseline system(USBL) is a kind of acoustic positioning technology now in wide use. This technique is more convenient than other baselines in view of its small aperture size and the easiness to install. However, the USBL has a low accuracy in a long-range operation because of its small aperture size. This paper proposes a method that improves the positioning precision by optimizing the traditional four-element array. The method requires fewer array elements, or makes it less difficult to build the transmitter as compared with the existing improvements of the USBL array. At the same time, for the application of the new positioning algorithm, this paper proposes a phase compensation formula. The simulation analyses show that the new array can improve the target positioning accuracy by nearly eight times as compared to the traditional ultra-short baseline array in, to achieve the high-precision positioning of distant targets.