Abstract: In carpet tufting process, the fluctuation of yarn tension is the main reason that causes uneven of carpet surface, so it is very important to stabilize the yarn tension. The expression equation of yarn tension is deduced when the yarn passing through the pulling roller and the mechanism of adjusting yarn tension by pulling rollers is got as follows: the pulling rollers can be viewed as a combined motion composed of many small cylindrical rollers rotational and translational movement and the contacting number of teeth with yarn keeps changing during the rotation of pulling rollers. Thus, wrap angle of yarn on the pulling rollers will change, which results in the change of yarn tension. Then, the relation between the total wrap angle and the center-to-center distance of two rollers is deduced with triangular geometry method, and the total wrap angle  varying with changing parameters is computed by using MathCAD software. Finally, through computation and analysis, the theoretical principle for adjusting yarn tension using pulling rollers is determined. This study will provide a reference for engineering practice.