Abstract: Fine imaging of target is significant for the identification of underwater targets. At present, the multi-beam imaging sonar and strip synthetic aperture sonar are the main methods to obtain images of small underwater targets. The target images are mainly characterized by highlight spots, and the results of observing the target from different directions are different, which brings difficulties to the identification and confirmation of targets. In order to solve this problem, a signal processing method using circular synthetic aperture sonar for underwater acoustic tomography of small underwater targets is proposed for improving the multi-angle fusion observation ability of sonar. The simulation and experimental data processing results show that the tomographic synthetic aperture sonar (SAR) imaging method can obtain the fine contour features of the target, which is conducive to the accurate identification of underwater small targets.