In this paper, we propose an analysis method for examining yarn cross-sectional structure. After obtaing yarn cross section photos, annular equal area yarn model and binary operation were used for image analysis and treatment. Then, statistic method was applied to analyze the distribution of fiber area in equal areas. The centroid position of the fiber and yarn were calculated, and the percentage values of the fiber area in each equal division against its circle (ring) area were obtained by using an ImageJ software. Finally a yarn sample was examined, and results show that this method is useful.