Underwater vehicles are commonly used in ocean industries. Because the sound wave is the most effective carrier for transmitting information underwater until now, underwater acoustic positioning system (UAPS) are used widely to locate underwater vehicles. Positioning accuracy and Multi-user positioning are the most important research hotspot being explored for current UAPS. To solve the problem within which signal design is a major issue. Limited bandwidth and Doppler shift effect influence the detection performance, user number of the UAPS. In order to solve these problems, we adopted spread spectrum communication and chose the Gold codes to be the pseudo random noise codes. Then serial search algorithm and parallel code phase search algorithm were introduced. Finally, the simulative experiments by MATLAB were implemented and the performance of the acquisition algorithm were analyzed.