Abstract: The theoretical analysis and experimental research on port/starboard discrimination in towed line array is proposed in this paper.Two methods for port/starboard discrimination by hydrophone triplets are introduced.By processing experimental data and analyzing experimental results,the theoretical results are verified.The algorithm is extended to broadband processing.The research results show that the method based on optimum beamforming for hydrophone triplets can be used to discriminate port or starboard of the target.And because of the simplicity of the method,it is expected to be implemented in practical towed line array sonar.