Abstract: The multi-aperture is an effective technique for increasing coverage rate of imaging in monostatic synthetic aperture sonar (SAS). In a special bistatic SAS (BiSAS) configuration with a fixed transmitter,the multi-aperture technique can also be used to deal with conflict between low space sampling rate and coverage rate of BiSAS. When the assumption of "stop-go-stop" is not effective,it will result in phase error that degrades the imaging quality. Based on the common dot-by-dot imaging algorithm,we discuss aperture movement during the signal transmitting time in a multi-aperture BiSAS system with fixed transmitter,and propose an improved dot-by-dot imaging algorithm with phase compensation. We also present and a new system design of multi-aperture BiSAS. Computer simulation results are given to show advantages of the improved algorithm and validity of the design.