Abstract: To solve the pure-angle localization problem of an underwater stationary beacon,a positioning method based on the pure azimuth information of a single array moving platform is proposed.Firstly,a group of two non-linear equations are established through the space angle information measured by the underwater unmanned observation platform at two widely separated locations;and then,the quasi-Newton iteration algorithm is used to calculate the stable numerical solutions of the non-linear equations.At the same time,the measurements are pre-and post-processed to improve the stability and accuracy of the positioning result.The proposed method is tested via the numerical simulations,where the shallow water multi-path environment is assumed and the conventional beamforming is taken for the angle estimation.Furthermore,the non-idea conditions,including the azimuth measuring errors,the sea depth measuring errors,and the changing relative locations between the platform and the beacon,are considered.The numerical simulations that when the standard deviation of the azimuth measurement error is 1 degree,the positioning error of the proposed method is about 3.5%.These results show that the proposed method is precise and robust,and has a potential to be applied to the acoustic positioning of the underwater stationary beacon.