The sewing function is composed of four basic mechanisms: 1. Take-up mechanism 2. Needle movement mechanism 3. Nutrition of the material 4-spindle The proper function of the sewing machine requires a delicate balancing between these mechanisms This paper is a computer simulation model that illustrates and introduces these mechanisms; it is used to predict sewing performance. Based on this simulation, a little understanding of the sewing machine can be achieved, which even leads to a tailor made sewing design and improved sewing process control. In this paper, in particular, the balance between the yarn supplied and the yarn needed is studied.Thread: The amount of yarn supplied by the take-up mechanism is said to be inside a threaded yarn. Thread Required: The yarn required is the yarn required within a stitch, which is controlled in the first place by the mechanism of the shaft (spool). Both properties change at a glance. In practice, if the amount of yarn required is much higher than the amount of yarn supplied, the result will be stitched stitches, that is, the knot of the ring can not be formed properly or even lead to tear tearing and thus stitching Will be incomplete.On the other hand, if the amount of yarn required is lower than the amount of yarn, it is likely that poor stitches are produced; a very loose thread in a knot or a broken ring may even result in the needle being broken. Using the simulated model, the instantaneous balance between threaded and thread required is studied quantitatively and it is stated that the balance between the thread and the desired thread can be changed instantaneously and by changing the design The parameters of the take-up mechanism can be optimized.