The purpose of this study was to examine the change of dyeing ability by K/S values, when dyed in different twisting processes and by one bath system and two bath system, to find possible ways of minimizing the color difference between cotton and polyester in composite yarn. The two types of composite yarn, which had one setting process(CP1) and two setting processes(CP2) were dyed with reactive/disperse dyes in both one bath dyeing system and two bath system. The dyeing ability according to the two different twisting processes was measured, and the values of the CP1 were higher compare to the values of CP2 in both one and two bath dyeing systems. This is because CP1 applied only one setting could shrink dyeing process at 130$^{circ}C$. This shrinkage increased the number of twists in the unit length and increased the yarn density, and this is the reason that the K/S values were measured higher than those of CP2. In wet shrinkage test, in opposition to CP2 only had 0.76$\%$ of the shrinkage rate, CP1 had 3.00$\%$ of the shrinkage rate. Also, the dyeing ability according to the two different dyeing methods was measured, and the values of CP1 and CP2 were both higher when dyed in two bath system. On the other hand, the color differences between cotton and polyester in composite yarns, were smaller for CP2 than that for CP1 and were also smaller in two bath dyeing system than in one bath dyeing system. Therefore, the ways of minimizing color difference between cotton and polyester in composite yarn are to apply enough setting in order to minimize shrinkage in dyeing process and to choose two bath dyeing system.