Abstract: For the problems in underwater image processing by traditional image detection methods,such as inaccurate location of objects regions,loss of object details and distortion of object shape,etc.,a new two-dimensional histogram based on edge information is proposed by utilizing the non-extensive property of Tsallis entropy.The improved particle swarm optimization(PSO) is used to search the best threshold value by maximizing the two-dimensional Tsallis entropy.The test results of some underwater images show that it is efficient to detect objects in underwater images.Comparing with traditional methods,the proposed approach shows better adaptability and robustness.