Abstract: The directivity function of twin-line array sonar can be used to identify left/right target. But the performance is limited by the distance between two lines and also exists the blind area for target identification. A method, which is based on the time-delay estimation between two line arrays, is proposed to identify left/right target. The method is robust with the variation of distance between two lines, the blind area is considerably decreased. The theoretical analysis results and realization method is described. An algorithm based on interpolation method for precisely estimating time-delay of two line array are derived, therefore the left-right ambiguity problem is solved.