Abstract: The energy's ratio of broadband is utilized for port/starboard discrimination in towed line array with hydrophone triplets in tradition.It can satisfy the need in most conditions except for two cases:One is low signal to noise ratio(SNR),and the other is that there is a stronger interfering target lied on the other side of the line array with approximate bearing.A new method called line-spectrum character extracting is proposed to discriminate port/starboard for these two cases in this paper,and the SNR needed for port/starboard discrimination is reduced sharply.Simulation and the sea-trial data are analyzed to show that the method is stable and valid,and it's expected to have application in practical towed line array sonar.A line-spectrum enhancing technology with lower calculation complexity and stable validity is proposed to ensure its application in lower SNR.