The invention relates to a roller drafting simulation method based on fiber arrangement in yarn. The method comprises the following steps that a roller jaw line serves as a head end of the yarn, the random arrangement of fiber in the yarn before drafting is generated and the unevenness of the yarn before drafting is calculated; according to the fiber accelerated point distribution, the accelerated point position of each piece of fiber is randomly generated, and the motion of each piece of fiber before acceleration is simulated; the drafting time is determined, and the motion of each piece of fiber after acceleration is simulated; the new arrangement of the fiber in the yarn after drafting is generated, the unevenness of the yarn after drafting is calculated, drafting results are analyzed by comparing the changes of the fiber arrangement in the yarn before and after drafting and the changes of the unevenness of the yarn before and after drafting, and a drafting technology is optimized. The fiber arrangement is introduced into the drafting simulation, the motion of each piece of fiber in the drafting process can be more visually reflected, comparative analysis is conducted on the changes of the fiber arrangement in the yarn before and after drafting and the changes of the unevenness of the yarn before and after drafting so that the drafting effect can be more visually judged, and accordingly, the drafting technology can be optimized.