Abstract: We proposed a fast back-projection algorithm for multi-receiver synthetic aperture sonar (SAS) in a shared memory environment. A two-dimensional dynamic data structure was used to keep the delay time and the compensation phase information was designed based on the characteristics of the back-projection algorithm, which helps to eliminate repeated delay time computation for the same range. In the shared memory environment, we combine the focusing operation for the near and far distance of the image scene to achieve a computation load balance. An imaging test performed on real SAS data confirms the proposed algorithm is accurate and efficient.