Thresholding is an important method of image segmentation and is extensively used in image processing for many applications.The fibrous material image captured from scanning electronic microscopy (SEM)shows the porosity surface structure characters of the material.To some extent,quantity analysis of material image is necessary for material study.In the paper,a method of image segmentation by artificial fish swarm algorithm based on two-dimensional gray histogram is presented after pretreatment.According to the maximum 2D entropy principle,the optimal combination of the parameters is searched,and the optimal threshold is determined by artificial fish swarm algorithm.Experimental results show that the proposed method gives better performance,and has a quick convergence rate.