Abstract: To accurately describe the geometric size of fibers in blended yarns, blending ratio, and spatial distribution and analyze the relationship between physical properties of blended yarns and these parameters, a new method is presented in this article. Take wool/viscose blended yarn as an example, the software ImageJ was used to analyzes the slice image of blended yarn cross-section, including quantitative description of the structural parameters such as blending ratio, relative radius of fiber distribution, fiber content distribution uniformity. On this basis, the relationship between structural parameters and the quality of the blended yarn is analyzed briefly, and the values obtained match with practical results. This provides important guidelines for quality control of blended yarn in practice.