Acoustic positioning systems are used to provide navigation and positioning for small submersible. Position detection rate and two factors affecting operations performed by submersible are important ; one is positioning period and the other is positioning error. Position detection rate has been discussed in the previous articles 1), 2). In this paper we present a method to asses positioning period from characteristic roots of motion equations of submersible, and we discuss factors affecting positioning error such as signal level, ambient noise, ray bending, sound velocity fluctuations, and submersible motion. Operating simulations are made to examine correlation between the two factors and motion control.