A yarn-changing method in a warping machine having yarn-changing units is disclosed. The yarn-changing method includes steps of (a) stopping a rotary creel having a plurality of working yarn packages and preparing one of the yarn packages for color changing; (b) sucking a yarn of the original yarn package; (c) clipping the yarn of the original yarn package and delivering it to a connecting unit; (d) taking a new color-changing yarn package from a storing creel by a swing arm for changing and then delivering a yarn of the new yarn package to the connecting unit; (e) connecting the yarns of step (c) and step (d); and (f) starting the rotary creel for wrapping, thereby changing one of working yarn packages with one of new color-changing yarn packages efficiently.