To solve the problems of low efficiency and long time-consuming in the recovery of unexploded ordnance underwater by LBL positioning system, and the problem of insufficient positioning accuracy by USBL system, an efficient single beacon underwater positioning system is designed. This system consists of two parts: one part is an ultrasonic beacon, which is launched into the water simultaneously with the experimental underwater shell; the other part is an ultrasonic receiving module, which is mounted on the UUV to detect the ultrasonic signals from the beacon. By capturing the ultrasonic signals emitted by the beacon multiple times along its pre-determined navigation path, and recording the corresponding time stamp data, the system can calculate the precise three-dimensional coordinates of the unexploded projectile using VLBL positioning technology. After a series of experimental tests, it has been proven that this single-beacon underwater positioning system can locate unexploded experimental projectiles within a range of 50 meters in lake environments, with a positioning accuracy that can reach the decimeter level. The successful development of this technology not only improves the detection efficiency and safety of underwater unexploded ordnance but also provides a new high-precision positioning method for other marine engineering operations, underwater archaeology, and seabed resource exploration.