Abstract: In oil and gas exploitation, cluster well technology can significantly reduce costs and improve efficiency. An effective adjacent well detection method can greatly reduce the risk of collision between adjacent wells. This study proposes a method to invert the 3D trajectory of an adjacent well using a scattered P-wave obtained by borehole azimuthal acoustic reflection imaging. After obtaining the scattered P-wave from the raw data of the target well using the wave field separation technology, the waveform data in an imaging profile can be obtained by the downhole acoustic directional reception technology. Migration imaging technology is then used to obtain the image of the formation in the imaging profile. Subsequently, by analyzing the images of the formation in the imaging profile of the different azimuths, the well spacing and azimuth of the target well can be determined. Finally, the 3D trajectory of the target well can be obtained by solving the inversion equation. This method was validated by processing the field data from a deviated well in a deep formation. The comparison of the inversion and actual trajectories of the target well demonstrated that the maximum deviation of the inversion trajectory is 0.9 m in the north-south direction, 0.78 m in the east-west direction, 1.45 m in the well spacing, and 2.48° in the azimuth. The field data inversion result demonstrated that the method can effectively use the azimuth reflection acoustic data to invert the 3D trajectory of an adjacent well, which indicates that the borehole azimuthal acoustic reflection imaging technology has great potential within the context of adjacent well detection.