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In the upsurge of unmanned and intelligentize, AUV technology and equipment have been widely concerned, which plays an increasingly important role in the sustainable utilization of marine resources. AUV technology is maturing, but the problem of short endurance has not been solved effectively. In order to obtain the multiple increase of AUV sailing distance and time, the world's maritime powers have carried out research on AUV autonomous underwater guidance and docking technology. Long distance acoustic positioning is the first action of AUV underwater guidance. When the acoustic ranging and positioning system are used for AUV underwater guidance, the acoustic ranging system is usually installed on AUV, and the acoustic beacon is installed on the guidance docking platform. When AUV is guided underwater, the acoustic ranging system sends an interrogation signal at the beginning of each ranging cycle. When the acoustic beacon on the guidance platform receives the interrogation signal, a reply signal is transmitted after the preset turnaround time of beacon. AUV underwater guidance has the phenomenon that acoustic signal transmission and reception are not in the same position. The conventional acoustic ranging and positioning method is based on the static target model, and the AUV motion in acoustic ranging is ignored. Simply use half of the two-way travel time as the observation value of the one-way travel time. This observation value is not equal to the one-way travel time between the beacon and the position of the AUV transmitting signal, nor the one-way travel time between the beacon and the location of the AUV receiving signal. For the approximate error of acoustic ranging observation model, theoretical derivation and simulation analysis are carried out. The influence degree and law of AUV motion on non identical position of acoustic ranging are obtained. Theoretical derivation and simulation analysis show that: The approximate error of distance measurement corresponding to the position of transmitting signal and receiving signal is equal in size and opposite in positive and negative. When the AUV speed is 1m / s, the maximum ranging error is -0.667m, and the ranging error decreases with the distance. In addition, the ranging error is proportional to the AUV velocity. When the relative horizontal position of AUV's straight track and beacon is different, the variation rule and numerical value of acoustic ranging error will not be affected. When the relative vertical position of AUV's straight track and beacon is different, the variation rule and numerical value of acoustic ranging error will not be affected. When AUV is guided from different directions, the AUV heading does not affect the variation rule and numerical value of ranging error. On the whole, the ranging error is not only proportional to the AUV speed, but also to the distance between the signal transmitting position and the beacon’s vertical line. But with the AUV approaching the underwater guidance platform, the influence is getting smaller, and the guidance accuracy is getting higher.