Abstract: A method of producing a high quality of yarn by an iron-heating apparatus, including the steps of: guiding a yarn to pass between upper and lower rollers, wherein the yarn is exited at a front nip in a twisting triangle area; guiding the yarn to enter to a groove of a heating main body of the iron-heating apparatus; heating the yarn along the groove to reduce a rigidity of the yarn so as to allow the yarn to be easily twisted to form an improved yarn with high quality; and enwrapping the improved yarn on a spun yarn tube. In addition, a counter frictional force is applied at the yarn through walls of the groove such that fiber on a surface of the yarn is further twisted to the yarn for minimizing hairiness.