Abstract: With the increasing development and wide application of acoustic imaging technology,the use of image sonar for underwater target recognition has become an important research direction in the field of underwater acoustic detection.According to the characteristics of forward-looking sonar images,a method of underwater target recognition is proposed and described as follows:Denoising and enhancing the sonar image and then segmenting it to obtain the area of the target;Extracting the regional shape features of the target;Using the particle swarm optimization (PSO) algorithm to optimize the regularization parameters and kernel parameters of the least squares support vector machine (LSSVM) and then to make a high-performance multi-classifier;Entering the characteristics of the target to be identified to achieve classification.Experiments show that the optimized least squares support vector machine can effectively identify the underwater targets with high accuracy.