Abstract: It is always an important problem of distinguishing the target's port or starboard in sonar signal processing of towed array.This paper presents a method that can improve the ability of restraining the port and starboard ambiguity via equalizing the amplitude and phase of the conventional beam forming output based on the unitary beam forming function.This method gets the weight value from the unitary beam forming function and then uses them to equalize the phase of the output of the conventional beam forming to cancelling the conjugate (mirror) output and get maximized port and starboard restrain ratio.The data simulation and sea trail data analysis proved that this is a simple and practical method and gave better result in improving the restrain ratio,especially on wide band condition.