Abstract: Passive Synthetic Aperture Sonar (PSAS), which uses the motion of the array to expand the virtual array to form a large aperture array, can significantly improve the azimuth resolution and weak target detection ability. The traditional Extended Towed Array Measurements (ETAM) method can estimate the phase correction factor in the array domain, but its performance is poor at low signal-to-noise ratio. In this paper, adaptive beamforming and ETAM synthetic aperture methods are combined to estimate the phase correction factor in the subarray beam space and perform adaptive beamforming. The simulation and experimental data show that the azimuth resolution and output signal-to-noise (SNR) ratio of the proposed method are 1.5° and 4.6 dB higher than those of the traditional ETAM method, and it is robust at low SNR and multiple targets, which provides strong support for passive weak target detection based on moving platforms.