The invention provides a speed transformation device for back-row bar guide rollers of a roving frame. Bars adopting the back-row bar guide rollers are actively quickly frozen forwards, so that accidental drawing caused by low cohesive force is overcome, the problem of large quality difference between the front row and the back row due to the accidental drawing is solved, and the problems of residual bars on the back raw are also correspondingly solved; and the cost is greatly reduced. The speed transformation device comprises a plurality of bar guide rollers on a bar guide frame of the roving frame, and is characterized in that the speed ratio of the multiple bar guide rollers in front of the last row of bar guide rollers is 1/1, and the speed ratio of the last row of bar guide rollers to the bar guide rollers in front of the last row is 55/54. According to the speed transformation device, the last bar guide roller is changed into an active conveying roller, so that the speed ratio of the last bar guide roller to the bar guide roller in front of the last roller is changed from 1/1 to 55/54, and the problem of large quality difference between the front row and the back row due to the accidental drawing is solved; the quality difference is reduced from 1.25 percent to 0.57 percent; meanwhile, the problems of the residual bars on the back raw are also correspondingly solved; and after the transformation is completed, the bar return amount is reduced by about 40 percent, and the cost is greatly reduced.