Abstract: In order to reduce the fluctuations of draw resistance and circumference of filter rods caused by the variation of tension in the tow generated when it is pulled out of an opened two bale, a constant tension control system was designed on the basis of closed-loop servo control principle. The system consists of a servo motor, a sensor, a tow control device, an additional tow opener, a control system and a display screen. The sensor monitors the tension in the running tow, compares it with the synchronized speed signal coming from filter rod maker, and controls the rotation speed of the tow control device to maintain a constant tow tension. The system was applied to ZL26C filter rod maker, and the results of a two-month test showed that the standard deviation of draw resistance of filter rods reduced by 20.62% and that of circumference of filter rods decreased by 50.00%, which indicated that the system significantly promoted the consistency of filter rod quality.