During the yarn manufacturing process, a fiber bundle undergoes drafting process which reduces linear density of the fiber bundle and enhances orientation of staple fibers. We have made a program using simplified algorithm expressing the motion of a two-velocity draft mechanism. To generate a virtual fiber bundle, a staple fiber diagram was made by disassembling a real fiber bundle use in the actual process and the acquired length distribution was used as program data. By executing the program with various parameters, such as draft ratio and gauge length among the many draft parameters which were variable in the actual process, it was possible to predict the characteristics of produced fiber bundle, such as mean linear density and its irregularity. By analyzing the data acquired by execution of the draft simulation program for the two-velocity model drafting process, similar tendencies as in the results of actual drafting experiment carried out by previous researchers could be determined, such as the relation between draft ration and mean deviation of linear density of the fiber bundle.