It is significant to measure the blending ratio of yarn in the practice of textile engineering. During the extraction of characteristic value, the paper puts forward acreage index, abnormity index and fluctuation index combining some literatures. By these morphologic indexes, it is convenient to construct corresponding eigenvector. It is the key point to discuss useful mathematical method for the cluster analysis during the measurement of the blending ratio. The paper sets up nonlinear optimal model for it. Using feasible fitness function and genetic algorithm, the paper gets fine results for cluster analysis.