Abstract: The platform motion error reduces the imaging performance of Circular Synthetic Aperture Sonar(CSAS).The slant-range error of CSAS can be estimated by the single-side echo,but the heave cannot be estimated by single-side echo in narrow-swath.Aiming at this problem,we propose a method of platform 3D-motion estimation and compensation based on echo signal.Firstly,it obtains the arrival time of CSAS by taking maximum values of CSAS target echoes from different observation angles.Secondly,the CSAS 3D positioning model is established based on the arrival time of multipoint targets.Then the three-dimensional coordinates of the sonar are estimated by using the Levenberg-Marquardt method.Finally,the position estimation results are combined with the time-domain back-projection imaging method to realize the imaging of the target.Simulation results show that the proposed method can accurately estimate the motion error of the sonar platform,and the estimation error of the spatial coordinates is less than 1/8 of the simulated signal wavelength,thus accurately compensating the echo time difference of CSAS array elements at different spatial sampling points,and significantly improving the imaging quality of the target.The experimental results show that the algorithm can compensate the motion of the circular synthetic aperture sonar without relying on the sensor data.Simulation and experimental results show the feasibility and effectiveness of the proposed method.