Among the existing underwater acoustic positioning methods, the long baseline positioning system is widely used because of its high positioning accuracy and good realtime performance. The least square method is the main method for solving long baseline underwater acoustic location. This method needs more than 4 reference acoustic beacons to solve the 3D position of the target acoustic beacon, which the number of reference acoustic beacons is large and the laying cost is high. This paper presents a long baseline underwater acoustic localization method with few acoustic beacons. This method uses an analytical algorithm to solve the distance equation, and uses three reference acoustic beacons to solve the coordinates of the target acoustic beacon. In this paper, the influence of the relative position between the reference acoustic beacon and the target acoustic beacon on the position calculation error is analyzed, and the distribution law of the target acoustic signal punctuation set satisfying the conditions is solved under different positioning error ranges. Theoretical analysis and simulation results show that, under the same distance measurement accuracy, the location distribution of reference acoustic beacon has a great impact on the target solution accuracy. In practical engineering, the layout of reference acoustic beacon should be adjusted according to the target trajectory to reduce its impact on the target position solution accuracy.