Abstract: A passive synthetic aperture based on phase correction algorithm for solving the port-starboard discrimination problem in the non-aligned towed twin-line array sonar is described. This method creates a virtual array through applying the estimated phase correction into one array of twin-line array, and because the synthetic virtual array is aligned with the other array in twin-line arrays, the right port-starboard discriminated results can be obtained by array processing based on the new synthetic twin-line array. The effect of proposed method would be shown by simulation and sea-trials results in towed twin-line array sonar. With low extra computational loads, the proposed method is easy to apply into the practice.