Evenness of the cotton/polyester(C/P) blend slivers produced with different processing conditions from a drawing frame is significantly affected on the quality of final spun yarns. In this study, we have compared experimental data with theoretical data on the evenness of C/P blend slivers, and established the optimum condition of drawing process, such as blending ratio, doubling strand and passage of drawing. The results obtained can be summarized as follows: The limiting irregularity ($CV_{h-lim}$) formula of the cotton sliver considered fiber fineness and fiber extent and the limiting irregularity ($CV_{h-lim}$) formula of C/P blend slivers were theoretically established. The limiting irregularity of blend slivers has decreased with increasing polyester fibers in blend slivers. Also, The limiting irregularity of blend slivers has decreased 0.1% with increasing doubling strand and 0.02% with increasing number of passage. The actual irregularity of C/P blend slivers has decreased 2.5% at 4 and 6 doubling, 0.9% at 6 and 8 doubling, respectively. Also, the actual irregularity has decreased 2.3% at 1 and 2 passage conditions, but it showed the uniform trend at 3 and 4 passage conditions. As the analysis result of irregularity index, the optimum condition of C/P blend slivers has estimated at 6 doubling and 2 passage of drawing processes.