The draft process is one of the most important processes in textile processes that determine the quality of spun yarn. In general, the parameters of drafting process include the number of fibers in sliver cross section, orientation of fibers, structure of silver cross section, surface shape of fibers, fiber length, distribution of fiber length, pressure of roller, roller gauge, draft ratio, etc. In this study, the fiber behavior in draft zone was simulated using the computer programming with the important parameters such as arrangement of fibers in silver, speed change model of floating fibers, distribution of fiber length, draft ratio, roller gauge, and effective contact length between high speed fiber and floating fiber. The correlation of irregularity with each parameter was also investigated.